Healthy streams contain a lot of living things! The three most dominant groups are fish, aquatic invertebrates (arthropods, mollusks, and segmented worms), and algae. Some of these are easy to spot, and others can only be seen through a microscope.

Let’s start with the very tiny organisms in the stream. Single-celled brownish-yellow plants called diatoms coat the pebbles on the stream bed. (That’s what makes them slimy and slippery!) These plants are food for the smallest animals which live in the stream.

The smallest animals are zooplankton, one-celled organisms. Water mites are barely visible to the naked eye. Worms like flatworms, annelides, nematodes, and leeches live in streams. Many insects begin their lives as larva in the quieter parts of the stream. Streams are home to tiny mussels, clams, and snails. Fish, from tiny minnows to larger species live in streams, eating insects and worms. Frogs, salamanders, and crayfish feast on smaller creatures in the stream.

Nature doesn’t have clean dividing lines between stream and land, and the ecosystems are highly dependent on one another. Turtles, snakes, frogs, and toads divide their time between the stream and shore. Water-dwelling creatures feed on bacteria and fungi from leaves which fall from trees nearby. We will learn more about the land surrounding the stream, the Riparian Buffer, at the next station.