The Met Office says the UK's marine heatwave is set to reach 'extreme' levels, with coastal waters running up to 5.3C above average and cod and mackerel already moving north

5.3C above seasonal average sounds abstract until you translate it into fish behaviour, and the pattern is consistent: cold-water species that would normally hold station around the UK coast through summer are relocating north rather than tolerating water that warm. Cod and mackerel moving isn't a subtle shift in where the best marks are, it's a real distributional change, which means marks that have reliably produced these species for years may simply be quieter this summer regardless of tide, bait or technique.

The knock-on effects are broader than just where fish are. Jellyfish numbers rising and octopus now breeding in British seas are the kind of ecosystem changes that follow sustained warm water, and they matter to anglers beyond the novelty value, more jellyfish generally means more line and gear fouling inshore, and shifting prey availability changes what predatory species are actually feeding on and when. A warm-water event this sustained doesn't just move fish, it restructures the food chain they're operating in.

For coarse and stillwater anglers this connects to a pattern already being reported this summer: spasmodic spawning and a shift toward feeding at cooler times, evenings, early mornings and overnight, rather than through the heat of the day. If your usual daytime session has felt unusually quiet, that's consistent with what's being reported elsewhere on both stillwaters and open coast, fish aren't switching off, they're switching their active hours to avoid the warmest water.

The practical read for anyone planning a session over the coming weeks: treat this as an ongoing event rather than a passing warm spell, since the Met Office is describing it as long-lasting and still intensifying rather than peaking and fading. If a coastal or stillwater session has underperformed against your normal expectations this summer, water temperature is a genuinely more likely explanation right now than technique, and shifting toward dawn, dusk or overnight sessions is a reasonable adjustment while the heatwave holds.