180 Million Water Tests Show Pollutants Hit Even Protected Rivers

"Protected areas do significantly reduce the number and frequency of pollutants. Nevertheless, adverse effects continue to occur frequently. Rivers and streams are open systems, so chemicals can also be carried by the current into ecologically valuable refuges," Lione explained.

In short: a protected status can't stop upstream contamination from flowing downstream.

What about PFAS, the "forever chemicals"?

Per- and polyfluoroalkyl substances — PFAS, a family of extremely persistent industrial chemicals — have risen to become the second most frequently detected pollutant group in the dataset. They showed up at roughly 60% of the sites studied. In urban areas, monitors detected an average of six to 11 different PFAS compounds per year.

"We still know relatively little about the effects of PFAS on aquatic ecosystems, even though more than 10,000 different PFAS molecules are in use. Their long-term and widespread presence, even in protected areas, is therefore particularly concerning," Lione said.

The knowledge gap here is large, and the researchers flag it plainly.

Which organisms suffer most?

Aquatic plants, the foundation of aquatic food webs, took the hardest hit. Aquatic invertebrates — animals without backbones, such as insects and crustaceans — came next, followed by fish.

Agricultural use significantly shaped environmental risk. Regulatory restrictions on the most problematic pesticides did produce measurable improvements for aquatic plants. Aquatic animals showed no comparable benefit.

"Our findings from this large-scale study highlight the far-reaching impacts of organic pollutants, especially pesticides, on aquatic ecosystems. At the same time, they show that risks can be reduced if particularly problematic substances are consistently replaced or phased out," Wolfram said.

Takeaway: regulation works when it targets the worst offenders, but it hasn't helped every group of organisms equally.

How much did the wider chemical scan change the picture?

Considerably. When the researchers included organic pollutants beyond pesticides, estimated environmental risk rose by 26% for fish and by 48% for aquatic invertebrates, compared with a pesticides-only analysis.

"Many earlier studies were likely unable to fully capture the actual environmental risks because chemical analysis covered only a limited subset of the substances present. To reveal previously unrecognized ecological pressures, environmental monitoring programs must be significantly expanded in the future, as the French program exemplifies," Lione emphasized.

The implication is uncomfortable: years of risk assessments may have understated the real pressure on rivers because they simply weren't looking for most of the chemicals present.

Takeaway: monitoring that only checks for pesticides misses a large share of the danger.

What happens now?

The study carries caveats typical of observational research. It relies on measured concentrations and known toxicity values, which remain incomplete for many substances — PFAS above all. Still, the findings point in one direction: protected areas remain valuable refuges for biodiversity, but they don't block chemical contamination on their own.

The data, the authors argue, make comprehensive environmental monitoring and firm regulation of problematic substances prerequisites for the long-term protection of aquatic ecosystems.

Publication: Danisa Lione et al., "Pesticides and organic pollutants pervasively threaten aquatic ecosystems, even in protected areas," Water Research (2027). DOI: 10.1016/j.watres.2026.127223.