A jump into some water is a big relief for a lot of folks on these hot summer days. But these days are deadly for critters who live in water all the time. The heat is starting to kill the fish in Missouri’s ponds and lakes.It’s not that the water is running low in some areas or that it’s hot; fish can dive to cooler, deeper water. The killer is lack of dissolved oxygen. The fish, in effect, suffocate because they can’t breathe and hot weather takes a lot of dissolved oxygen out of the water.The State Conservation Department’s Paul Calvert says the situation is aggravated when water owners try to kill off algae that flourishes in warm weather. Some impoundments aerate water to get more oxygen into it. But Calvert says that’s an expensive process that many private landowners can’t afford. The answer, he says, is to get the dead fish out of the water as soon as possible, because they need oxygen to decompose and that means less oxygen for the fish trying to survive. He says these conditions should last until the middle of next month, at least.