Brown trout start to die when water temperature hits between 22C – 25C for more than 7 consecutive days. In hot summers, a small number of sites in the New Forest, have recorded maximum water temperatures over 31 C - warmer than many heated swimming pools.
Some climate predictions indicate water temperatures will exceed the safe thresholds for river fish; and trees alongside riverbanks are a crucial part of the biodiversity of our waterways.
Salmon are also already under pressure, from sediment and pollution run-off, barriers to swimming up-river, lower flows and changes in habitat.
The annual fisheries report from the Environment Agency show a continued decline in salmon populations, with over 90 per cent of stocks in England’s principal salmon rivers assessed as being at risk, or probably at risk. At sea, marine survival of salmon has nearly halved over the last 20 years; making it more important that their freshwater habitat is improved, and protected.
In order to protect the future of salmon and trout stocks, there is a call for urgent action to Keep Rivers Cool by planting broadleaf native trees alongside river banks, creating dappled shading and stopping water from warming up.
Shade can reduce temperatures in small rivers by on average 2- 3C compared to un-shaded streams; and by more on hot summer days.
Now Keeping Rivers Cool is calling for action. Speaking on behalf of the KRC partnership, Diane Millis, from the Woodland Trust said: “We’re asking people who value our rivers to survey their local river bank, and look at specific areas which may need shade. Landowners, Rivers Trusts, anglers, farmers and ecological groups can all help. “
The KRC partnership is asking groups working in catchment areas to take up the challenge using a practical guide for planting along river margins, available on the Woodland Trust website.
The manual gives step by step instructions for planting, species selection and location, ensuring the right balance of shade for fragile river ecosystems.
The Keeping Rivers Cool partnership can provide landowners and groups working in catchment areas with first hand specialist advice; and the Woodland Trust can also offer generously subsidised trees. Shade maps showing locations along English rivers which are at risk from direct sun and may need more riparian shade can be accessed here via The Rivers Trusts
“Figures show that stocks are already decreasing and if we don’t start taking the temperature threat seriously, iconic fish like salmon, will face even more serious decline. Rivers, and the ecosystems they support, are one of our most valuable natural resources,“ said Ms Mills.
