Circular No. 95/2025/TT-BNNMT guiding the assessment of the carrying capacity of surface water environments for rivers and lakes

CIRCULAR

Guidelines for Assessing the Carrying Capacity of Surface Water Environments for Rivers and Lakes 

Pursuant to the Environmental Protection Law No. 72/2020/QH14 amended and supplemented by Laws No. 11/2022/QH15, No. 16/2023/QH15, No. 18/2023/QH15, No. 47/2024/QH15, No. 54/2024/QH15, and No. 146/2025/QH15;

Pursuant to the Government Decree No. 08/2022/NĐ-CP dated January 10, 2022 detailing certain provisions of the Environmental Protection Law, amended and supplemented by the Government Decree No. 05/2025/NĐ-CP dated January 6, 2025;

Pursuant to the Government Decree No. 35/2025/NĐ-CP dated February 25, 2025 stipulating the functions, tasks, powers, and organizational structure of the Ministry of Agriculture and Environment;

At the proposal of the Director of the Environmental Agency;

The Minister of Agriculture and Environment issues this Circular guiding the assessment of the carrying capacity of surface water environments for rivers and lakes.

PART I
GENERAL PROVISIONS

Article 1. Scope of Regulation

This Circular guides the assessment of the carrying capacity of surface water environments for rivers (including: rivers, streams, canals, ditches, ravines, creeks) and lakes (including: lakes, ponds, lagoons), hereinafter referred to collectively as the assessment of the carrying capacity of rivers and lakes.

Article 2. Applicability

This Circular applies to state management agencies, organizations, and individuals involved in the assessment of the carrying capacity of rivers and lakes.

Article 3. Principles for Assessing the Carrying Capacity of Rivers and Lakes

1. The assessment of the carrying capacity of rivers and lakes must ensure systematicity based on river basins and water sources.

2. For rivers, when conducting the assessment of carrying capacity, they must be divided into sections of the river for evaluation.

3. The division of river sections, determination of water usage purposes, selection of flow rates, and choice of surface water quality parameters and pollutant parameters from various wastewater sources for assessing the carrying capacity of each section of the river must ensure systematicity for each river and river system.

4. The assessment of the carrying capacity of rivers and lakes must be conducted for each pollutant parameter.

5. The assessment of the carrying capacity of rivers and lakes is based on the characteristics of water usage purposes, the self-cleaning ability of water sources, the scale and nature of current and planned wastewater sources according to economic and social development plans.

6. The assessment of the carrying capacity of rivers and lakes shall be carried out during the periods specified in the surface water quality management plan under the Environmental Protection Law or determined by the competent authority responsible for announcing carrying capacity pursuant to Clause 1, Article 15 of this Circular when any of the following circumstances occur:

a) There is a revision to the economic and social development plan related to wastewater discharge activities;

b) There is a project or construction involving water extraction, utilization, or wastewater discharge that significantly alters the flow regime or water quality of rivers and lakes;

c) As required by the competent authority responsible for announcing carrying capacity pursuant to Clause 1, Article 15 of this Circular.

Chapter II
ASSESSING THE CARRYING CAPACITY OF RIVERS AND LAKES

Article 4. Rivers and Lakes Subject to Assessment of Carrying Capacity

1. Rivers listed in the inter-provincial and intra-provincial river basin directories, and inter-provincial and intra-provincial water source directories issued by authorized state agencies.

2. Lakes listed in the inter-provincial and intra-provincial water source directories issued by authorized state agencies.

3. For rivers and lakes not covered by the provisions of Clauses 1 and 2 of this Article, the People's Committee of provinces and centrally-administered cities shall decide on the assessment of carrying capacity based on the importance of the rivers and lakes to economic and social development, requirements for water resource protection, environmental protection, biodiversity conservation, and cultural value preservation related to water resources.

Article 5. Division of Rivers for Assessing Carrying Capacity

1. The division of rivers for assessing carrying capacity shall be based on the following criteria:

a) The location of inflows and outflows on the river; the topographical conditions of the river basin;

b) The function of the water source and the purpose of water usage of the river; the location of water extraction and utilization facilities, wastewater discharge facilities; the location of reservoirs and water regulation facilities on the river;

c) The maximum length of river sections affected by salinity intrusion corresponding to a salinity level of 4.0‰ or higher for river sections influenced by tides;

d) The current water quality status and requirements for protecting, improving, and restoring water sources; requirements for protecting religious, spiritual activities, cultural values, biodiversity, and tourism development;

đ) For inter-provincial rivers and rivers with transnational characteristics, in addition to the criteria set forth in points a, b, c, and d of this clause, administrative boundaries at the provincial level and national borders must also be considered.

2. River sections are defined as follows:

a) A river section is defined by two consecutive cross-sections based on changes in flow rate, water usage purposes, water source functions, requirements for protecting, improving, and restoring water sources, and has a length of 10 kilometers or more, except in cases provided for in points b, c, and d of this clause;

b) For river sections affected by tides where the maximum length of salinity intrusion corresponds to a salinity level of 4.0‰ or higher, they are divided into separate sections;

c) In cases where river sections pass through areas such as urban zones, concentrated residential areas, industrial zones, craft villages, areas receiving multiple wastewater sources, polluted water areas, biodiversity conservation zones, cultural and historical value conservation zones related to water resources, these sections may be considered for division into separate sections;

d) In cases where river sections have a length less than 10 kilometers and do not fall under the circumstances provided for in point b and point c of this clause, they may be combined with adjacent sections or divided into separate sections.

Article 6. Determining the purpose of water use to assess the carrying capacity of rivers and lakes

1. The purpose of water use and water quality objectives for river sections and lakes shall be determined based on the approved water resources planning and environmental protection planning by competent state authorities. In cases where river sections or lakes have multiple purposes of water use, the purpose with the highest water quality requirements shall be selected.

2. In cases not specified in Clause 1 of this Article, based on the actual exploitation and utilization status of river sections and lakes, the competent authority responsible for announcing the carrying capacity pursuant to Clause 1 of Article 15 of this Circular shall consider and determine the purpose of water use and water quality objectives for river sections and lakes for assessment purposes.

Article 7. Parameters for assessing the carrying capacity of rivers and lakes

1. The carrying capacity of rivers and lakes must be assessed for each of the following parameters: COD, BOD₅, total nitrogen, total phosphorus, and other parameters prescribed in Clause 2 of this Article.

2. Based on national technical standards for surface water quality, effluent discharge standards, the purpose of water use, water quality objectives, scale, nature of effluents, and requirements for protecting water sources and the environment for each river section and lake, the competent authority responsible for announcing the carrying capacity pursuant to Clause 1 of Article 15 of this Circular shall consider and decide on specific additional parameters for assessment purposes as appropriate.

Article 8. Methods for assessing the carrying capacity of rivers and lakes

1. Methods for assessing the carrying capacity of rivers include:

a) Direct assessment method: Assessing the carrying capacity of rivers is conducted based on the maximum limit of each parameter according to national technical standards for surface water quality, flow rate, and the results of water quality analysis of the river section, as stipulated in Clause 3 of Article 9 of this Circular; the direct assessment method is applied to river sections that have been surveyed and found to have no direct effluent discharges.

b) Indirect assessment method: Assessing the carrying capacity of rivers is conducted based on the maximum limit of each parameter according to national technical standards for surface water quality, flow rate, and the results of water quality analysis of the river section, as well as the flow rate and analysis results of effluents discharged into the river section, as stipulated in Clause 4 of Article 9 of this Circular;

c) Modeling assessment method: Assessing the carrying capacity of rivers is conducted based on the maximum limit of each parameter according to national technical standards for surface water quality, flow rate, and the results of water quality analysis of the river section, as well as the flow rate and analysis results of effluents discharged into the river section and the process of joining the flow and changes in pollutants;

d) The assessment of the carrying capacity of rivers is carried out in accordance with the provisions of Article 9 of this Circular.

2. The assessment of the carrying capacity of lakes is carried out in accordance with the provisions of Article 13 of this Circular.

3. Based on the principles for assessing the carrying capacity of rivers stipulated in Article 3 of this Circular and information and data on flow rates, water quality of rivers, flow rates, and water quality of effluent sources, the competent authority responsible for announcing the carrying capacity pursuant to Clause 1 of Article 15 of this Circular shall consider and decide on the application of appropriate assessment methods for each river section and river system, except for cases stipulated in Clause 4 of this Article.

4. For river sections affected by tides as stipulated in Point b Clause 2 of Article 5 of this Circular, only the modeling method shall be applied for assessment.

Article 9. Assessment of the carrying capacity of rivers

1. Principles for assessing the carrying capacity of rivers:

The carrying capacity of a river section depends on the pollutants of concern, flow rate, and pollutant load passing through the river section. The method for assessing the carrying capacity of a river section is based on the relationship between point sources, diffuse sources, pollutant loads of existing water quality parameters in the water source, and the loss of pollutants due to processes occurring within the river section.

2. Building calculation scenarios:

a) Base scenario: A scenario built to calculate the carrying capacity based on the average low-flow flow rate and the maximum load of surface water quality parameters calculated according to the value limits specified in national technical standards for surface water quality corresponding to the current water quality classification level at the time of assessment, detailed in Clause 1 of Article 10 of this Circular;

b) Scenario based on water use purpose: A scenario built to calculate the carrying capacity based on the average low-flow flow rate and the maximum load of surface water quality parameters calculated according to the value limits corresponding to the water use purpose in national technical standards for surface water quality.

3. Direct assessment method:

Evaluation formula: L_tn = L_tđ - L_nn

Where:

L_tn is the carrying capacity for each pollution parameter, measured in kg/day;

L_tđ is the maximum load of each surface water quality parameter for the river section and is determined according to Article 10 of this Circular, measured in kg/day;

L_nn is the load of each existing water quality parameter in the river section's water source and is determined according to Article 11 of this Circular, measured in kg/day.

4. Indirect assessment method:

Evaluation formula: L_tn = L_tđ - L_nn - L_tt + NP_tđ

Where:

L_tn is the carrying capacity for each pollution parameter, measured in kg/day;

L_tđ is the maximum load of each surface water quality parameter for the river section and is determined according to Article 10 of this Circular, measured in kg/day;

L_nn is the load of the existing water quality parameter in the river section's water source and is determined according to Article 11 of this Circular, measured in kg/day;

L_tt is the load of the pollution parameter in the effluent and is determined according to Article 12 of this Circular, measured in kg/day;

NP_tđ is the maximum load of the pollution parameter lost due to processes occurring in the river section, measured in kg/day. The value of NP_tđ depends on each pollutant, characteristics of each water source, topographical conditions, and is determined based on actual conditions, or may not be considered if reliable data is insufficient for assessment.

5. Assessment using the modeling method:

a) Based on the characteristics of the river flow of the river section, river, or entire river system, information and data on flow, water quality, and effluent sources, the competent authority responsible for announcing the carrying capacity pursuant to Clause 1 of Article 15 of this Circular shall consider and decide on selecting an appropriate model for assessment;

b) The model used to assess the carrying capacity of rivers must have the capability to simulate hydraulic conditions and water quality consistent with water quality calculations and self-purification capacity when biochemical reactions significantly affect the results;

c) The model used to assess the carrying capacity of rivers must be calibrated and verified before use;

d) Hydraulic condition simulation must establish a computational network and cross-sections, set boundary conditions;

đ) Water quality simulation must establish input data including: river network system; boundary conditions; point source and diffuse source pollution data;

e) Water quality simulation must simulate the diffusion and transformation processes of pollutants in the aquatic environment;

g) The simulation results of water quality from the model are used to assess the carrying capacity of rivers according to the calculation formula stipulated in Clause 3 of this Article.

Article 10. Determining the Maximum Load of Water Quality Parameters

1. Calculation formula: L_tđ = C_qc x Q_s x 86,4

Where:

C_qc is the limit value of the water quality parameter according to the national technical regulation on surface water quality, unit of measurement is mg/l; for parameters with multiple limit values according to the classification levels of water quality specified in the national technical regulation on surface water quality, C_qc is determined based on the following two cases:

- In the case of calculating according to the baseline scenario prescribed in point a, Clause 2, Article 9 of this Circular, apply C_qc according to the limit value corresponding to the current water quality status at the time of assessment, specifically: if the current water quality is at level A, choose C_qc according to the threshold of level A; if the current water quality is at level B, choose C_qc according to the threshold of level B; if the current water quality is at level C or D, choose C_qc according to the threshold of level C; in cases where appropriate measures are taken to treat water for each pollutant parameter ensuring compliance with water quality standards for intended use, C_qc may be applied according to a lower level than the current water quality status at the time of assessment but not lower than level C;

- In the case of calculating according to the scenario based on the intended use of water prescribed in point b, Clause 2, Article 9 of this Circular, apply C_qc according to the limit value corresponding to the appropriate level for the intended use of water planned for that section of the river (A or B or C); in cases where appropriate measures are taken to treat water for each pollutant parameter ensuring compliance with water quality standards for intended use, C_qc may be applied according to a lower level than the level prescribed for intended use but not lower than level C;

Q_s is the flow rate of the section of the river being assessed and is determined according to the provisions of Clause 2 of this Article, unit of measurement is m³/s;

The value 86,4 is the dimensionless conversion factor (converted from units of mg/l, m³/s to units of kg/day).

2. The flow rate of the section of the river being assessed is calculated based on the average low-flow discharge according to hydro-meteorological observation data.

Article 11. Determining the Load of Current Water Quality Parameters in Water Sources

1. Calculation formula: L_nn = C_nn x Q_s x 86,4

Where:

C_nn is the result of analyzing the water quality parameters and is determined according to the provisions of Clause 2 of this Article, unit of measurement is mg/l;

Q_s is the flow rate of the section of the river being assessed and is determined according to the provisions of Clause 2 of Article 10 of this Circular, unit of measurement is m³/s;

The value 86,4 is the dimensionless conversion factor (converted from units of mg/l, m³/s to units of kg/day).

2. The results of analyzing the water quality parameters are determined at cross-sections of the section of the river being assessed and based on the average value of the analysis results of at least 10 samples during the dry season, with sampling frequency suitable for the variation of low-flow discharge; in cases where there are monitoring data on water quality from hydrological, water resources, and environmental monitoring activities of competent state agencies at the section of the river being assessed, consider using these data for evaluation. The location of water sample collection at cross-sections is carried out as follows:

a) At the end cross-section of the section of the river being assessed for direct method application;

b) At the start cross-section of the section of the river being assessed for indirect method application.

Article 12. Determining the Load of Pollutant Parameters in Wastewater

1. The wastewater sources entering the section of the river include two main sources: point source pollution and diffuse source pollution. The formula for determining the total load of pollutant parameters in wastewater:

L_tt = L_t + L_d

Where:

L_tt is the total load of pollutant parameters in wastewater;

L_t is the load of pollutant parameters from point source pollution;

L_d is the load of pollutant parameters from diffuse source pollution.

2. The formula for determining the load of pollutants from point source pollution:

L_t = C_t x Q_t x 86,4

Where:

C_t is the result of analyzing the pollutant parameters in wastewater discharged into the section of the river and is determined according to the provisions of Clause 3 of this Article, unit of measurement is mg/l;

Q_t is the maximum flow rate of wastewater discharged into the section of the river and is determined according to the provisions of Clause 4 of this Article, unit of measurement is m³/s;

The value 86,4 is the dimensionless conversion factor (converted from units of mg/l, m³/s to units of kg/day).

3. The results of analyzing the pollutant parameters in wastewater are determined based on the average value of the analysis results of at least four wastewater samples with a sampling frequency of not less than one sample per day (regardless of whether it is the dry or flood season). In cases where wastewater has been monitored according to legal regulations, consider using these monitoring data for evaluation.

4. The maximum flow rate of wastewater is determined based on the monitoring results of wastewater flow rates according to legal regulations or the maximum flow rate recorded in environmental permits, environmental registrations, or equivalent legal documents on environmental protection.

5. In cases where there are multiple wastewater sources discharging into the section of the river, the determination of pollutant loads is conducted separately for each wastewater source.

6. In cases where economic and social development plans have identified wastewater sources, flow rates, and expected pollutant parameters to be discharged into the section of the river being assessed, additional loads of each pollutant parameter should be considered and determined. The values of each pollutant parameter for assessment are determined based on the limit values stipulated in the technical regulations on wastewater.

Article 13. Evaluation of the Load-Carrying Capacity of Reservoirs

1. For reservoirs on rivers:

a) In cases where the reservoir operates under daily operation mode, the load-carrying capacity of the reservoir is evaluated based on the evaluation of the load-carrying capacity of the river section with the reservoir according to the methods and formulas specified in Article 9 of this Circular;

b) In cases where the reservoir does not operate under daily operation mode, the load-carrying capacity of the reservoir is evaluated using the formula:

M_tn = (C_qc - C_nn) x V_h x 10^-3

Where:

M_tn represents the load-carrying capacity for each pollutant parameter of the reservoir, measured in kg;

C_qc represents the limit value of the water quality parameter according to the national technical regulation on surface water quality suitable for the purpose of water use in the reservoir, measured in mg/l;

C_nn represents the analysis result of the water quality parameter of the reservoir and is determined according to Clause 2 of this Article, measured in mg/l;

V_h represents the volume of the reservoir and is determined based on the average dry season volume of the reservoir, measured in m³.

2. The analysis results of the water quality parameters of the reservoir are determined based on the average value of the analysis results of at least 10 samples during the dry season, with a frequency appropriate to the variation in the reservoir's dry season volume; if the reservoir has been monitored for water quality according to the provisions of the law, such data may be considered for evaluation purposes.

3. For reservoirs not falling under the cases stipulated in Clause 1 of this Article, the evaluation of the load-carrying capacity of the reservoir shall be carried out according to the provisions of point b, Clause 1 of this Article.

4. For reservoirs stipulated in point b, Clause 1 and Clause 3 of this Article, based on the characteristics of the reservoir, information on water quality data and discharge sources, the competent authority shall consider and decide to apply modeling methods to evaluate the load-carrying capacity as prescribed in Clause 1 of Article 15 of this Circular. The model for evaluation must be calibrated before conducting the evaluation.

Article 14. Requirements for Evaluation Results of the Load-Carrying Capacity of Rivers and Reservoirs

1. The evaluation results of the load-carrying capacity at each river section must be substantiated and clearly explained regarding the segmentation of the river, determination of the purpose of water use, determination of flow rate, evaluation parameters, and selection of evaluation methods prescribed in this Circular.

2. The evaluation results of the load-carrying capacity of the reservoir must be substantiated and clearly explained regarding the determination of the purpose of water use in the reservoir, determination of the reservoir volume, evaluation parameters, and selection of evaluation methods prescribed in this Circular.

3. The load-carrying capacity for each pollutant parameter (the permissible discharge load of each pollutant parameter that can continue to be discharged into the aquatic environment, also known as the effluent discharge quota) of the river section and reservoir is specifically expressed as numerical values, where values greater than 0 indicate remaining load-carrying capacity, and values less than or equal to 0 indicate no remaining load-carrying capacity.

4. The evaluation results of the load-carrying capacity of the river must be compiled and presented on a river system diagram; a list of evaluated river sections must be established, wherein each evaluated river section must include the following main contents:

a) Name of the river section, name of the river, name of the river basin;

b) Length of the river section, administrative boundary of the area where the evaluated river section is located;

c) Evaluation results of the load-carrying capacity of the river section for each evaluation parameter according to the scenarios specified in Clause 2 of Article 9 of this Circular, presented on a zoning map corresponding to each parameter.

Article 15. Announcement of the Load-Carrying Capacity of Rivers and Reservoirs

1. The Ministry of Agriculture and Rural Development announces the load-carrying capacity of inter-provincial rivers and reservoirs. Provincial People's Committees and municipal people's committees directly under the central government announce the load-carrying capacity of intra-provincial rivers and reservoirs.

2. The evaluation results of the load-carrying capacity are announced on the official website of the competent authority responsible for announcement as stipulated in Clause 1 of this Article. The content of the announcement includes an administrative document regarding the announcement of the load-carrying capacity of rivers and reservoirs, accompanied by the evaluation results of the load-carrying capacity meeting the requirements set forth in Clauses 3 and 4 of Article 14 of this Circular.

Chapter III
IMPLEMENTATION

Article 16. Transitional Provisions

1. For tasks and projects evaluating the load-carrying capacity of rivers and reservoirs that have been approved and implemented prior to the effective date of this Circular, the competent authority shall consider calculating and announcing the evaluation results of the load-carrying capacity according to the formulas and scenarios prescribed in this Circular.

2. For tasks and projects evaluating the load-carrying capacity of rivers and reservoirs that have been approved but not yet implemented prior to the effective date of this Circular, the competent authority shall consider adjusting the content according to the provisions of this Circular for implementation.

Article 17. Effective Date

1. This Circular takes effect from February 15, 2026.

2. From the date this Circular takes effect, the following regulations cease to be effective:

a) Circular No. 76/2017/TT-BTNMT dated December 29, 2017, issued by the Minister of Natural Resources and Environment, detailing the assessment of wastewater reception capacity and water source load-carrying capacity of rivers and reservoirs;

b) Article 4 and Article 82 of Circular No. 02/2022/TT-BTNMT dated January 10, 2022, issued by the Minister of Natural Resources and Environment, detailing certain provisions of the Law on Environmental Protection, amended and supplemented by Circular No. 07/2025/TT-BTNMT dated February 28, 2025, issued by the Minister of Natural Resources and Environment, and Circular No. 07/2025/TT-BNNMT dated June 16, 2025, issued by the Minister of Agriculture and Rural Development.

Article 18. Responsibility for Implementation

1. The Ministry of Agriculture and Rural Development, People's Committees of provinces and centrally governed cities shall be responsible for directing the implementation of this Circular.

2. Relevant organizations and individuals shall be responsible for implementing this Circular./.