Water quality if very important to an aquatic insect. In order to have a long, healthy life, there must be oxygen and not a lot of pollution in the water. Insects help scientists determine water quality in a stream or a river. If stoneflies, mayflies, dobsonflies live near or in the pond, it means that the water is of good quality and there isn't hardly any pollution in it. Now if the water is somewhat polluted, you should notice alderflies, dragonflies, and damselflies. If the water is very bad and heavily polluted, you'll only see small insects such as a black fly or an aquatic snail inhabit that environment.

Sources:
http://pathfinderscience.net
http://biology.usgs.gov