The heatwave currently baking the UK and Ireland is now officially the hottest on record – another sign that our climate is changing. Across the country, action is being taken to protect human health. Red weather warnings are in place for London and parts of southern England, and a yellow warning has been issued for the Republic of Ireland. Kent is now contending with a hosepipe ban, to conserve water supplies.
But what about our rivers? This kind of weather creates a pressure cooker for freshwater habitats, especially those without much shade. As the water heats up, it loses dissolved oxygen, putting many fish and invertebrates at risk of suffocation. Those that remain will often be listless, leaving them unable to feed or escape from predators.
Brown trout, for example, are happiest in water that is colder than 15°C. Other salmonids, like grayling and Atlantic salmon, have similar needs. By the time the water hits 20°C, these fish will be seriously stressed. Even with a careful catch-and-release angling approach, there is a high chance that a protracted tussle could be fatal.
We all want to protect our wonderful wild fish from harm. So if you’re going fishing in the next few weeks, we recommend carrying a thermometer and taking a temperature reading from the river. Even if the evenings bring slightly cooler breezes, or rain raises the water level, the river temperature may still not have returned to a level that’s safe for fishing.
If the water is around 16 – 18°C, the fish may be starting to struggle with the heat; bring them to your net quickly, keep them in the river (ensuring they stay wet at all times), and skip taking a photo. They may also need more time to recover before swimming off strongly. But if the water is 19°C or more, then it’s best to head home.