When Is Water Too Warm to Fly Fish | Why I Haven't Fished for Months
- James
- Aug 26
- 6 min read
Updated: 3 days ago
Great Brown trout caught
Quick Summary
At FFF we haven't been fishing for months. It's not down to being lazy or losing interest. It's been that hot and dry it's just not fair on the fish. So we've been giving it a miss. Doesn't mean I've been sat around doing nothing though, been trying to learn to double haul and sorting all my gear out ready for when things pick back up.
Why High Water Temps Stop Summer Trout Fishing
It's been mad this year. Hardly any rain, drought pretty much everywhere, and my usual stillwater's have taken a hit from it. I'm a member of Barnt Green Fly Fishing Club, Davo's a member there too. Fantastic club, fish welfare's top priority there, barbless fishing all year round, and it's run by top people. Even there though, the weeds grow super fast in this heat. Green algae comes with it too. Makes fishing a nightmare on top of everything else.
We've both said the same thing to each other more than once this summer, the water's just not right for it. Walk round the bank and you can see it. Water levels well down from where they'd normally be, algae sat thick on top in the warmer spots. Not the kind of conditions either of us want to be casting into. Nobody's been fly fishing for trout there for ages either, not just me and Davo, everyone's given it a miss.
Where the Fish Actually Go,What Is a Thermal Refuge?
Here's something I found genuinely interesting looking into all this. Trout don't just sit there and suffer in the heat. They go looking for what's called a thermal refuge, a cooler patch of water somewhere in the lake or river that's a few degrees below everything around it. Could be a spring feeding in from underground, a shaded inflow, a deep hole, anywhere the water's noticeably colder than the main body.
Once it's genuinely hot, trout pack into these refuges in big numbers, sometimes right on top of each other. Sounds like it'd make them easier to catch, but it's the opposite. That's exactly when you should leave them well alone. A fish crammed into one of these last safe pockets is already right at its limit. Disturbing it, wading near it, or worse, hooking it, could easily finish it off. Ethical anglers avoid these spots in a heatwave rather than target them.
Explains why you can walk a length of bank in this weather and see next to nothing. They haven't disappeared, they've just found somewhere better to be until it cools down.
Why They Stop Feeding Anyway
Even if you did find fish, they're not really interested in eating in this weather. Once the water's up around 19 to 20°C, trout stop feeding much, sometimes stop altogether. Chasing food takes energy, and when they're already stressed and short of oxygen, they'd rather save it than bother with your fly.
It's not just the trout either. The insects they feed on slow right down in extreme heat too, so hatches get thin on top of everything else. Double whammy really, less appetite and less food about at the same time.
Whatever feeding does happen tends to get squeezed into first thing in the morning or last thing at night, when the water's had a chance to cool off a bit. Midday's pretty much a write off in this kind of heat.
Water too warm to Fly Fish, What Water Temperature Is Too Hot for Trout?
Trout like it cool, somewhere between 10 and 16°C. Once the water gets past 18 or 19°C they start struggling. When the water too warm to fly fish, oxygen levels drop and trout drastically reduce their feeding. Here is a quick reference table to check your local water temperatures before heading out:
Here's a quick reference if you're checking your own water:
10°C to 16°C : Happy fish, feeding well, plenty of oxygen about. Get out there.
18°C to 19°C : Starting to struggle, feeding drops off. Only fish early morning if at all.
20°C and up : Proper trouble, low oxygen, real risk to the fish. Leave it, even catch and release.
Stillwater's get it worse than rivers. The top layer heats up in the sun while it stays cooler underneath, so the trout end up pushed right down deep chasing cooler water. July and August are always the worst months for stillwater trout because of this.
Get much past 20°C and the fish are properly stressed. Brown trout stop growing at around 19.5°C, and if it stays too hot for too long it can genuinely kill them. Even if you hook one and let it go carefully, a fish that's already stressed and short of oxygen often doesn't make it.
UK Drought Fishing 2026: What The Rivers Are Like Right Now
Rivers aren't much better than the stillwater's if I'm honest. A quarter of river monitoring sites in England are classed as exceptionally low right now, mostly down south and east. Reservoir storage has dropped to around 62%, well below where it should be for this time of year, and it's been falling week on week.
There's been over 20 confirmed algae incidents and over 20 confirmed fish deaths linked to the drought so far this year. Some rivers picked up a bit after recent rain, but nowhere near enough to actually fix anything. Forecast's saying it's more likely than not we stay dry right through to October too. So it's not looking like a quick turnaround.
Not Just Me
Loads of fisheries have closed for a bit this summer because of it. Some reservoirs have banned catch and release altogether, no safe way to do it right now. Fish kills this year are apparently the worst since 2014.
Big tackle shops seem to be doing fine though. Angling Direct actually grew their sales this summer despite the drought. Worth remembering they sell all types of fishing gear though, not just fly fishing, so that doesn't tell you much about how the fly fishing side of things is doing specifically. My guess is the smaller shops that specialize in fly fishing are probably struggling a lot more right now.
If you're using the downtime to sort your own kit out, Sportfish is always my go to for leaders, tackle, and general fly fishing gear.
Keeping Busy While I Wait
It's a real shame really, fly fishing in the English countryside in summer with great weather sounds fantastic on paper, a few beers, a picnic, good company on the bank. Just sounds idyllic. Just doesn't work like that when the water's in this state. Its Depressing ! 😒
Between practicing the double haul and sorting through gear, I've also been going through old fly boxes I hadn't touched in ages, restocking the patterns that were running low and binning off the ones that had seen better days. Bit of a satisfying job when you've got the time for it, though I'd still rather be out casting than doing work on my own kit.
When I'll Be Back
Once we get some proper rain and the lakes cool down, I'll be straight back out. Until then it's just a waiting game. Honestly, it's been genuinely stressful not being able to get out fishing. It's normally my time to switch off and relax, so not having that has been tough. Pike season should be starting back up again soon, though it might end up being a bit late this year given how things have gone. Fingers crossed it's not too much longer.
A Few Common Questions
What water temperature is too hot for trout?
Anything past about 18 to 19°C and they start struggling. Get up around 20°C and most trout are properly stressed.
Is it OK to fish in a heatwave?
Better not to, honestly. Even catch and release can end up killing a fish if it's already stressed and short of oxygen. Best to just leave them be until it cools down.
Will this affect the fishing season?
Could do. If the drought carries on, the start of pike season and how the rest of trout fishing goes this year could both end up pushed back a bit.
The Verdict
Not fishing isn't fun, but it's the right thing to do this summer. Give the water and the fish a break. Plenty more good days coming once this weather breaks.
Tight lines. 🎣
Related reading
Thanks James | Fishing Field Fork
Comments