How Healthy is Your Stream?

Every spring, summer, fall, and, optionally, during winter, 180 ANS volunteers fan out across Montgomery County and Washington DC to monitor our local streams. They wade into the water to collect small organisms that live among the rocks on the bottom, hide in the spaces between fallen leaves and roots, and cling to plants growing in the water. The technical term for these organisms is “benthic macroinvertebrates” because they have no backbone and live on the bottom of streams. Many of them are aquatic insects.

The monitors identify the organisms, record their findings, and return them to the stream. We can compute a stream health score for the monitoring visit based on the diversity and types of organisms we find. That’s because some of them are more sensitive to pollution and environmental stress, such as high water temperatures and low dissolved oxygen, than others. Streams with greater diversity and more sensitive organisms receive higher scores than those with little diversity and more tolerant organisms.

As a rule, streams in forested and rural areas usually have better water quality than those in developed areas. This map shows the relative health of the stream sites we monitor. Each monitoring site has been given a color-coded rating based on the average of its stream health scores for the years 2012-2016. Check out the map made by our ANS summer intern Christian Schluter: how healthy is your stream?
On July 14, we submitted a report of all of our data for the years 2012-2016 to the Maryland Department of the Environment (MDE), including the map above. MDE will use this information to help make planning decisions like whether the stream is meeting water quality standards and whether it should be restored.

If you are interested in learning more about monitoring with ANS, we invite you to attend our upcoming introductory Stream Science classes in September, or contact me at to find a team that monitors near you so you can go and observe. Classes and monitoring are open to people of all ages.

About Cathy Wiss

Cathy Wiss is the Coordinator of ANS' 26-year Water Quality Monitoring Program. She teaches classes, manages our database and equipment, and coordinates the nearly 200 volunteers who collect data in the field.
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