Lovely weather, isn't it? Perfect for lying in a hammock, hand trailing through the grass as you swing back and forth, occasionally sipping some iced tea. Too hot to move, though, or to eat; best just to lie still until the evening brings some respite, and maybe a cocktail.
In the world of fly-fishing, deep at the bottom of lakes and rivers, this is what the fish are thinking, too. OK, so they don't have the hammocks and the iced tea, or the grass. And it's debatable whether they can actually think at all. But it's too hot for them to move, or eat very much. And quite frankly, you're buggered if you think you're going to net a trout in this weather.
Non-fishermen don't understand this, bless them. They try to find something to say to you, hoping the weather will provide common ground. "Nice day for fishing," they say to me 125 times a day in the summer. No, it's not. It's a nice day for getting grumpy thinking about fishing; it's a nice day to clean your rod and reorganise your fishing waistcoat while drinking Pimm's (one must stay hydrated) so you can actually find anything in its myriad pockets, but it is not a day to go fishing.
However, this time of year is precisely when non-fishers decide they want to see what all the fuss is about and ask you to take them fishing. You think "river, picnic, feet up, snooze", but they're thinking, "Hunter-gatherer, fish, BBQ later, get a tan at the same time." It's a recipe for woe. It doesn't matter how much you tell them that in hot weather the water of a lake stratifies (imagine a B52 cocktail), rendering the top 18 inches or so too hot for a fish to breathe, so they go as deep as possible. Or that fish are like human beings: in hot weather they get lethargic and don't move, and this makes fishing really tough. No matter how often you tell your non-fisher friends that their chances of catching a fish on a hot day are zero, but that they could practise their casting, they refuse to listen and go out there full of hope. And an over-optimistic novice fly-fisherman coupled with blistering heat equals a day that will end in big, hot tears, and with the most mature of men stamping their feet in frustration.
You can go fishing when it's really, really hot, but your day has to start very early: you need to be on the bank by 6am to have a few hours at it. On a river, breakfast for the fish is caterpillars and beetles, scooped off the water's surface as they fall off the leaves, so I'd start with a bright green caterpillar pattern. But as soon as the sun is out, it's time to push your hat over your eyes, lie back and stop fishing until dusk. At sundown, you'll almost certainly get a big hatch of caddis fly. So use a big dry fly such as the G&H, which is bushy and fun to fish with, especially for beginners, because they can see what they're doing.
Fishing on a lake in summer is hard for even the most accomplished fisher, and can be immensely frustrating. Rivers afford more opportunity for "dark water" - cooler waters in the shade - while on a lake you can find yourself having to cast in almost impossible situations, seeking out what little shade there is. Another problem can be algae: if you see this, go home. I've fished on lakes, in deepest summer, where the water was thick with algae (the microbes are photo-sensitive, which is to say they react with the sun, and they reproduce at an alarming rate). Fishing in such conditions is hopeless. I did it only because we were literally fishing for our supper - and that of another 12 people. (We ended up going to Waitrose.)
But even without this handicap, if you are to have any chance at all of rousing fish, you need to get a bit vulgar on a lake in summer (shhh, don't tell anyone), using such things as muddlers and boobies, and generally getting desperate and stooping to depths - both literal and metaphorical - that you'd prefer no one else knew about. A good picnic is a must here, preferably with a large pork pie and a not insubstantial amount of chilled alcohol to help you philosophise.
It's not a pretty sight and it's not a side of fishing that you want anyone new to the sport ever to have to see. Fly-fishing, when it's hot, can get very ugly indeed.