From Sichuan’s Rivers to the World: A Data Case Study on Phosphorus Pollution and Water Governance in Southwestern China

In my home province of Sichuan, two rivers tell an important story about water pollution: the Minjiang and the Tuojiang River.

They are not just local rivers. They are part of the upper Yangtze River system, flowing through areas with cities, agriculture, industry, and millions of people. For O.WATER, they are also a useful case study for a global question: how can a region improve water quality when the remaining pollution problem is not one single pipe, but a mixture of urban wastewater, industrial sources, agricultural runoff, river management, and legacy pollution?

This article shares the first stage of our open data case study. It is descriptive, not causal proof. We are not claiming that one policy or one project alone caused the improvement. Instead, we are using official data to understand what changed, where the remaining pressure is, and what kind of governance method other regions might learn from.

Why Total Phosphorus Matters

The main pollutant thread in this case is total phosphorus, often written as TP.

Phosphorus is a nutrient. In the right amount, it supports life. In excess, it can drive eutrophication: algae blooms, low oxygen, damaged ecosystems, and water that becomes harder and more expensive to treat. This is not only a Chinese issue. From lakes in North America to rivers in Europe and agricultural basins around the world, phosphorus pollution is one of the most common water-quality challenges.

For rivers under China's GB 3838-2002 surface-water standard, the Class III limit for total phosphorus is 0.2 mg/L. For lakes and reservoirs, the Class III limit is stricter, at 0.05 mg/L. In this case study, we are careful not to mix those two standards.

What We Analyzed

For this first release, we only used official-source data that we could trace back to specific public pages from Sichuan's ecological environment authorities or national standard sources. Missing numbers were left missing. We did not generate, simulate, estimate, or fill any data points.

The dataset currently includes:

- official surface-water quality snapshots for Sichuan Province;

- Minjiang and Tuojiang basin good-rate records;

- class distribution data for Jan-May 2025;

- official average pollutant concentrations for Jan-May 2025;

- seeded section-level examples where total phosphorus was listed as the pollution indicator;

- source notes for water-quality standards and governance policies.

The most important limitation is that monthly reports and official briefings can use different assessment scopes. We keep those records separate instead of merging them into one smooth trend line.

Good-rate Snapshots

Finding 1: Sichuan's Assessed Surface-Water Quality Is Now Very High

In the official records entered so far, Sichuan's assessed surface-water quality is already at a high level.

For Jan-Dec 2024, all 345 national and provincial assessed sections were reported as Class I-III, giving a good-rate of 100%.

For Jan-May 2025, the monthly-report scope gave a good-rate of 99.1%. A separate adjusted briefing scope gave 99.4%. These two numbers should not be merged because they use different official reporting scopes, but both point to the same broad picture: the assessed sections are overwhelmingly within Class I-III.

This matters because "good" in this context means Class I-III. It does not mean every water body is clean, and it does not mean every pollutant problem has disappeared. It means that under the official single-factor evaluation system, the assessed sections met the Class I-III standard.

Sichuan Surface-water Class Distribution

Under the adjusted Jan-May 2025 briefing scope, Sichuan had:

- 76 Class I sections;

- 179 Class II sections;

- 88 Class III sections;

- 2 Class IV sections.

That means 343 of 345 sections were Class I-III, or 99.4%. It also means Class I-II sections made up 255 of 345 sections, or 73.9%.

Finding 2: Minjiang Looks Stable in the Current Records, While Tuojiang Remains the More Important Story

The Minjiang records currently entered show a consistently high good-rate. In the records we have entered for 2020, Jan-Jul 2023, Jan-May 2024, full-year 2024, and Jan-May 2025, Minjiang is reported at 100% good-rate.

Tuojiang is more complex, and that is exactly why it is important.

The entered official records show:

- 2020 press release record: 93.8%;

- Jan-Jul 2023 national sections: 33 of 37 good, or 89.2%;

- Jan-May 2024 national sections: 35 of 37 good, or 94.6%;

- full-year 2024 national sections: 37 of 37 good, or 100%;

- Jan-May 2025 monthly-report national sections: 34 of 36 good, computed from official counts as 94.4%;

- Jan-May 2025 adjusted briefing: 98.3% for Tuojiang.

The key point is not that every number moves perfectly upward. The key point is that Tuojiang shows why water governance has to be basin-specific. A province-level average can look excellent while one basin still needs more attention.

Good-rate Comparison between Minjiang and Tuojiang

Finding 3: Total Phosphorus Is Still the Pollutant to Watch

The Jan-May 2025 official briefing reported Sichuan's average total phosphorus concentration as 0.050 mg/L, down 5.39% year on year.

That is encouraging, but it does not mean phosphorus no longer matters. Phosphorus can be highly local. A province-wide average may look low while specific tributaries, industrial areas, agricultural zones, or urban rivers still face pressure.

The same briefing also reported year-on-year declines in several pollutants, including ammonia nitrogen, CODMn, COD, and total phosphorus. This suggests that the remaining challenge is not only about one number, but about continuing to control multiple pollution pathways.

Pollutant Concentrations

In seeded section-level examples from December 2020, total phosphorus was listed as the pollution indicator for multiple Minjiang-system and Tuojiang-system sections. These examples are not a complete census. They are included to show why TP is a meaningful thread for deeper analysis.

TP Exceedance examples

The Governance Methodology: Why This Case Is Useful Beyond Sichuan

The most transferable lesson from Sichuan is not a single engineering project. It is a method.

The method is:

1. measure the water quality carefully;

2. identify the dominant pollutant and the dominant source in each basin or tributary;

3. choose methods that match the actual source;

4. keep monitoring after intervention;

5. adjust the plan when the data show remaining pressure.

This sounds simple, but it is powerful. Many water problems fail because the solution is too generic. A river affected by urban sewage needs different tools from a river affected by agricultural runoff. A tributary affected by phosphorus industry or phosphogypsum stockpiles needs different tools from a mountain source river that is already mostly clean.

In Sichuan's Minjiang-Tuojiang context, the official policy and planning documents point to several categories of action:

- industrial phosphorus control, including phosphogypsum stockpile management, cleaner production, wastewater separation, and stricter discharge control;

- urban wastewater upgrades, including improved treatment capacity and higher discharge standards;

- rural wastewater and toilet-wastewater treatment;

- agricultural nonpoint-source control, including livestock waste management and fertilizer reduction;

- river-channel and ecological restoration, including black-odor water treatment, source interception, sediment or internal-source management, and wetlands;

- governance mechanisms such as the river-chief system, one-river-one-policy planning, monitoring capacity, and basin-level ecological compensation.

The logic is source matching. If phosphorus comes mainly from an industrial stockpile, the solution must control leakage, runoff, storage, and reuse. If it comes from wastewater, treatment plants and pipe networks matter. If it comes from agriculture, the solution must involve fertilizer use, livestock waste, and land management. If the problem is spread across a basin, then monitoring and accountability become just as important as construction.

Why This Matters to the World

Total phosphorus and eutrophication are global problems. Many places are trying to clean rivers after decades of urbanization, agriculture, and industrial development.

Sichuan's experience is useful because it shows a practical governance mindset:

Do not start with a slogan. Start with data.

Do not assume one river is the same as another. Identify each basin's main source.

Do not use one solution everywhere. Match the solution to the source.

Do not stop after a project is built. Keep monitoring.

For O.WATER, this is the core lesson. Clean water work becomes stronger when young people, communities, policymakers, and scientists can all look at the same evidence and ask better questions.

What We Will Do Next

This is the first release of our case study, not the final version.

Next, we plan to expand the dataset with more section-level official records for Minjiang and Tuojiang, city-level annual reports from places such as Neijiang, Deyang, and Meishan, and more official policy documents that show exactly how each pollution source was addressed.

We will also keep the most important rule of this project: every number must be traceable to an official source. If a value is missing, we leave it missing. Clean water data should be clean data.

Sources and Data Note

This article is based on official public sources, including Sichuan surface-water quality reports and briefings, Sichuan ecological environment documents, and GB 3838-2002 surface-water quality standard information. This is a descriptive data case study. It does not prove causality between any single policy and any single water-quality outcome.