Published 17/10/2026 By William Turtle-Clark

The first quarterly report from a continuous water quality monitoring device on the River Wye has revealed that severe summer heat and algal growth created dangerous conditions for local fish populations.

The floating buoy, launched last June in a joint project by AquaWatch and Haigh Environmental, collects data on water temperature, dissolved oxygen, pH, turbidity, and electrical conductivity every 15 minutes, generating over 35,000 individual readings across the quarter.

According to the report, high water temperatures presented the greatest pressure on aquatic life. The warmest recorded reading reached 27.9°C at 4:00 PM on 26 June, with approximately 1 in 10 readings exceeding 24°C, a threshold known to trigger severe thermal stress in native salmon and trout, reducing growth rates, impairing cellular function, and forcing fish to seek cooler, deeper waters while feeding less.

The monitoring data also highlighted significant fluctuations in oxygen and pH levels linked to intensive seasonal plant and algal growth. Almost half of all recorded oxygen readings dropped below the 9 milligrams per litre minimum recommended for salmonid species, with around 6 in 10 of these lower readings occurring overnight when photosynthesis ceases. Meanwhile, pH levels routinely exceeded the ideal upper limit of 8.0, regularly approaching 9.0 on August afternoons and peaking at 9.2.

AquaWatch and Haigh Environmental confirmed that monitoring reports will be published on a quarterly basis, with the next dataset scheduled for release in December.