I saw that in the news about the swans and waterfowl being taken ill.
While the temps were at their highest, I tried spraying the duckweed back off the surface of our pond to try and keep it oxygenated, which is what one fishpond website recommended doing. Our tadpoles did seem to vanish overnight, but I am hoping they made the transformation into froglets before it got too warm.
I used to do a lot of fly fishing and studied the way water in lakes behaved, and how the trout behaved within the lake, it was necessary to find out how far down the fish were, so, A pond or lake has three layers of water, the Hypolimnion is the lower part of the water, the Epilimnion is the upper layer of the water, and sandwiched between them is the Thermocline, the sun heats up the surface water which travels along with the breeze and goes down, the cold water from below rises to the surface not in a vertical way but more like a radiator it rises at the opposite end of the pond/lake, so the top layer of water is warm the bottom layer is cold but the Thermocline remains a constant temperature, where fish go to in extremely hot weather, if a pond or lake becomes lower because of evaporation during hot weather then the Thermocline could be non existent because of the reduced depth and so be a contributory factor along with a bloom of algae to the death of the fish at Stodmarsh. Duncan