Despite extreme heat and humidity warnings, I made it out for 2 days of fishing during the hottest days we've had all season. The ground temperature hovered around 36 Celcius, felt like it was closer to 50 with the humidity. Last time I felt this sort of weather was when I spent a summer in Texas a number of years ago.
When fishing during a heat wave, there are a few essential ways to stay alive:
1) Drink plenty of water. I can easily drink close to 1 liter per hour.
2) Apply lots of sunscreen, even if you're not directly in the sun all day.
3) Sit in the shade. As I'm still fishing from the shore, I can afford to sit back and relax until the fish bite.
4) Take frequent dips in the water. The water temperature will be a good 10 degrees less than the outside temperature, and water will cool you down about 25 times faster than outside air of the same temperature.
So there I am, sitting in my bathing suit in the shade sipping some cold beer while intermittently gulping down water. Set up my rods for carp, wondering how they will react to the heat. Surprisingly enough, the fishing was quite good. Fishing with my son the first day, we hooked 7 carps in 4 hours, ranging from 8 to 20 lbs.
Returned the following day with my wife. She caught her first channel catfish after about 20 minutes or so, a nice 14 lb "river monster". I posed for the pic, as she'd rather have me hold it and get "slimed" instead of her.
I was kind of surprised to see a channel cat that size hit during a bright sunny day around noon, especially in the blistering heat. I usually don't get those until after dark. During the following 4 hours, we managed 6 carps, ranging from 10 to 24 lbs.
Another aspect I found interesting, was the quality of the fight each fish gave. While I first expected them to be a bit lethargic in warm water, I noticed that they were trying harder than usual to hug the bottom. After getting in the water, I figured out that the thermocline started about 6 or 7 feet down, which would explain why they wanted to stay in their comfort zone.
While some fishermen dread heat waves based on the species of fish they target and the style of fishing they choose, I've learned to enjoy them while they last, by targeting bottom feeders while staying as comfortable as possible.