This natural event should illustrate to all that coldness is a price you pay for good quality water for both humans and fish. This means that with a temperature increase, there is more growth, more eating, more excreting, more reproduction, more algae blooms, more decomposition, etc. Unfortunately, there is a threshold above which quality aerobic life can no longer exist in warm waters. Since oxygen is needed for complete breakdown of organic matter, the decrease in dissolved oxygen that is associated with the higher water temperatures often cannot accommodate the decomposition that is necessary to keep up with the recycling of such growth. In short, the complications that can arise in lake ecology by higher water temperatures are very intricate.
Most aquatic organisms have temperature range specifications and preferences.
Obviously though, highly desirable fish, quality microscopic algae and even humans do not benefit by higher average water temperatures. The heat of the earth, sunlight, and unnatural industry are the most common sources of heat in a body of water. Some sources can be controlled and others cannot.