When the lake/river water starts to get hot if you take the minnows out of cold water from a cooler and put them in a lake or river that has warm/hot water it will be a shock to them and kill them. When I buy minnows I gradually change temp of water in my minnow cooler by taking out and adding water till the water is no longer cold. When I get to where I'm fishing I put a little warm water from lake into cooler to get minnows use to it. Of course I always have arreator going. You don't have to worry about water being to warm for a few more months.