Streams are a crucial part of Earth’s circulatory system. They carry sediments, nutrients and other materials into rivers and lakes and on to the ocean. Healthy streams foster healthy rivers, lakes, and estuaries. But streams are also vital ecosystems on their own, providing wildlife habitat, protecting us from floods and supplying much of our drinking water.

Many freshwater fish depend on streams for habitat. So do diadromous fish like salmon, river herring and American eels—fish that spend part of their lives in freshwater and part in the ocean. Many insects, often forgotten in the aquatic world, also need stream habitat, especially as larvae.  Aquatic insects form an important part of stream food webs.  As indicator species, they can also act as “canaries in the coal mine.”  The mix of insect species indicates whether a stream is healthy or not. Delicate insects like mayflies thrive only in gentle, unpolluted streams. When ecologists find a stream rich with mayfly larvae, it’s a good sign the stream is healthy. When mayflies disappear, the stream could be in trouble.

But what does a healthy stream look like? Stream health goes beyond reducing pollution, though this is critical. Keeping streams healthy also means protecting banks and channels from erosion. High-energy currents, which can appear during storms or floods, can destroy habitat and create steep, high banks. Impervious surfaces like roads or driveways can intensify currents by keeping soil from absorbing rain water before it rushes into streams. Sometimes, watersheds with only 2 percent impervious surface can see sensitive insect populations plummet.

At SERC, ecologists track stream species with underwater SONAR cameras and analyze insect data to predict stream health. They’re also working to restore damaged streams with volunteer citizen scientists. Explore the projects below to learn more.