So when the health of Wales’ rivers changes, it matters to us.

New analysis from Afonydd Cymru looks at 25 years of water quality records from Natural Resources Wales (NRW), covering the period from 2000 to 2025.

And the findings paint a mixed picture.

There has been real progress. Several important pollutants have fallen across Welsh river catchments, and treated effluent being discharged into rivers is generally cleaner than it was in the early 2000s.

But not everything is improving.

Some pollutants are falling

Afonydd Cymru analysed NRW water quality records, looking at long-term changes, in Welsh rivers. To make the comparison meaningful, they only compared sites monitored in both the early 2000s and early 2020s.

Across the catchments where a reliable trend could be established:

• Ammonia fell in 8 of 14 catchments, with none showing an increase.
• Orthophosphate, a form of reactive phosphorus, fell in 7 of 14, again with none increasing.
• Nitrate fell in 6 of 14 catchments, with the Dee the only catchment showing an increase.

That sounds encouraging, and it is. But another important measure tells a different story.

One measure is heading in the wrong direction

Biochemical oxygen demand, or BOD, is used as an indicator of organic pollution in water. According to the analysis, BOD is worsening in five of the seven catchments where a trend could be verified: the Cleddau, Dee, Teifi, Usk and Wye. None of those seven catchments showed an improving trend. That is particularly significant because some of these rivers have some of the highest levels of environmental protection, including designation as Special Areas of Conservation.

Sewage treatment has improved, but it still affects rivers

The data also tells us something important about wastewater treatment. Effluent discharges, mainly from sewage treatment works but also including some industrial discharges, are measurably cleaner than they were in the early 2000s. Suspended solids decreased in 13 of 14 catchments where a reliable trend could be identified, while ammonia fell in 9 of 14.

However, cleaner does not mean impact-free.

compared recent river samples taken between 2021 and 2025 from above and below the same sewage treatment works. At all eight works where there was enough data, ammonia and orthophosphate levels were higher downstream, typically around 1.5 to 2.5 times higher. Nitrate was also higher downstream at seven of the eight sites. It demonstrates something that can occasionally get lost in the wider debate about river health: investment in wastewater treatment can make a measurable difference, but sewage treatment works continue to contribute nutrients to the rivers receiving their discharge.

And sewage isn't the only pressure affecting our rivers.

Agricultural runoff, storm overflows, roads, industry, land use and the natural characteristics of the river catchment all influence what ultimately ends up in the water.

But are we monitoring enough?

Perhaps one of the most concerning findings isn't about pollution at all. It's about how much monitoring is taking place. They found significant reductions in river monitoring, including within designated catchments.

For example, when looking at BOD monitoring, the Dee lost 89% of its monitoring sites between 2006–2010 and 2021–2025, while the Teifi lost 75%. Between 2021 and 2025 there were 288 river sites sampled for BOD, compared with 1,025 for ammonia. That creates an important problem. If we want to know whether our rivers are getting healthier, we need enough good-quality, consistent data to tell us.

Reduced monitoring doesn't necessarily mean river quality has deteriorated, but it can make changes much harder to identify and understand.

Rivers need a whole-catchment approach

One of the clearest messages from the analysis is that there isn't a single cause, or a single solution, to the problems facing Welsh rivers. Investment in the water industry has delivered measurable improvements. At the same time, significant pressures remain, arguments that the next approach to improving Wales' rivers should include stronger river monitoring, better understanding of pollution coming from land, shared accountability between the organisations and sectors affecting our rivers, and more integrated management of whole catchments.

For paddlers, that bigger picture matters.

We see these rivers at water level. We paddle them throughout the seasons, introduce new people to them, run clubs and events on them and, in many cases, have been part of these river communities for decades.

Protecting our rivers means understanding what's happening throughout the catchment, identifying where pollution is coming from and making sure decisions are based on reliable evidence.

There has been progress over the last 25 years. But the data also shows there is still a long way to paddle.

About the research

This blog is based on analysis published by Afonydd Cymru in November 2026, using Natural Resources Wales Water Quality Archive data from 2000–2025.

The original analysis also draws on Welsh Government, Natural Resources Wales and water regulator publications. For more information click HERE.