Record water temperatures recorded by our citizen scientists across the catchment
A warming planet means warming rivers. River activists in Ludlow carry an overheating planet down to the Teme.
Last weeks record heatwave not only scorched the land, but also the river, with 10% of our tests recording temperatures exceeding 25℃, and more than half (57%) exceeding 20℃, between the 21st and the 28th of June. Many of these tests broke records for their test locations, and two broke our highest record temperature across the river.
The Environment Agency’s sonde at Ross-on-Wye recorded temperatures as high as 27.7℃ on Friday the 26th of June, 3.7℃ warmer than the same time last year, and 5.7℃ higher than the year before. This temperature also breaks the previous peak temperature by 1.2℃, record coming from much later in the season.
The river is reaching the same temperatures we would usually expect of heated swimming pools (26-30℃), not open water.
Across the month of June the average temperature has been 1.15℃ higher than the 2022-2025 June average, and a shocking 1.79℃ above the 2022 average. This increase has resulted in the Wye and Ithon having average temperatures above 20℃, increasing strain on fish and the ecosystem as a whole. All our results can be seen on WyeViz.
NRW and angling groups recommend fishing should stop from 20℃ (especially for Trout and Salmon), and all fishing should stop (other than Carp) from 25℃, due to post capture mortality rates increasing exponentially with temperature. Much of the Wye is now exceeding these safe temperatures, and with more heatwaves likely, the ecosystem and its fish could be put into an even more precarious position.
Looking at these temperatures and the very high levels of E.Coli that we found at the Warren (Hay-on-Wye) on the 25th June, a worrying picture emerges. With these added climate stresses the Wye will need our help, not just to stay clean, but also to stay cool.
This latest heatwave feeds into into a longer term trend of rising river temperatures, with the average temperature of the Wye catchment from Jan-Jun being 0.48℃ higher this year than the 2022-2025 average (Jan-Jun), 0.38℃ than the 2025 average and a massive 0.54℃ increase from 2022 and 2023.
How can you help? Keep an eye out for for dead fish, especially during heatwaves, and report them and other incidents to NRW in Wales and the EA in England or call 0800 80 70 60. This data will give us a better idea of fish mortality, where it occurs, and why. You can also sign up to be a citizen scientist here.
The highest temperatures the Wye Alliance recorded (high to low) between June 21st and 28th were; Wye at Monmouth Show Ground, The Gamber at Audits Bridge, Wye at Glasbury Bridge, Monnow at Tregate Bridge, Monnow at Kentchurch, Monnow at Rockfield, Wye at Clifford, Wye at Hay-on-Wye (Wyeford Road Slipway), Wye at Byford, Wye at Victoria bridge.
Write up by Forrest Lawrence, Citizen Science Coordinator and Science Communicator
