Remember, though, that pollution tolerant organisms can be found in both polluted and unpolluted waters. These are perhaps the most important component of a healthy aquatic habitat. If there are plants, there will undoubtedly be some forms of insects and other small organisms feeding on them or their remains. Insects, then, are a major link in the food chain. These insects typically emerge from the water to become adults, going through various stages as they grow.
Most insects go through either complete metamorphosis or incomplete metamorphosis.
Incomplete metamorphosis is typical of many insects. This is where a freshly hatched insect does ressemble the adult stage in some but not all ways. Dragonflies are good examples of incomplete metamorphosis. At birth, the dragonfly ressembles the adult somewhat, but has no wings and slightly different mouthparts, and lives completely under water, unlike the adult who will never again swim. As it grows, it sheds or molts it's skin.