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Want to know if a stream is healthy? Ask the animals that call it home.

Like the canary in the coal mine whose silence once warned workers of toxic gases, the county's smallest inhabitants, from the tiny fairy shrimp to the foot-long brown trout, each provide a snapshot of the world in which they live.

Scientists with the county's environmental protection department have been looking to aquatic insects, fish, crayfish and freshwater mussels for 15 years to learn how they have adapted to their environment and whether they can continue to survive.

"We wanted to understand what were the cumulative impacts that are on the stream, and the best way to look at that is to look at the things that are actually living in the streams," program supervisor Keith Van Ness said. "It shows everyone what the county looks like at this point in time."

The county's team of aquatic biologists collects data on insects, worms, mollusks and shellfish in the spring and fish in the summer, and they began monitoring reptiles and amphibians during both seasons this year. After checking water temperature and pH levels, they record the number and diversity of organisms they find and any anomalies, such as black spots on fish indicating parasites.

The rural upcounty has high quality streams teeming with life, while poor water quality is more common in highly developed areas with lots of impervious surfaces, particularly areas that developed before stormwater management systems were widely used.

Watersheds are monitored on a five-year cycle, though the county's four special protection areas, highly sensitive sites potentially threatened by planned development, are monitored twice a year. The data is shared with other government agencies and used to guide development.

Monday, aquatic biologist Rachel Gauza and four interns combed Ten Mile Creek in Boyds, one of the highest-quality streams in the county, for signs of life. Fish were temporarily stunned and placed into buckets of oxygenated water until they could be weighed, recorded and released into the stream.

"We try to take every precaution to not impact the fish and return them to the stream safe and healthy," Gauza said as the interns scooped up green sunfish and blue ridge sculpins in their nets.

The Audubon Naturalist Society shares data from its 18 water quality monitoring sites, including Ten Mile Creek, with the county and trains residents to monitor streams in their communities, program coordinator Cathy Wiss said.

"Most of the stream is really protected," Wiss said. "There's not a lot of impact from development, from pavement, the things that tend to reduce the number of living organisms that can grow in the stream."

The Department of Environmental Protection has been moving from providing a snapshot of stream health to looking at how to restore what has been lost. Van Ness pointed to the successful restoration of Sligo Creek in Silver Spring, which had as few as three species of fish in some parts when the collaborative project began in 1990. Van Ness said when he was growing up in the area, he would see fish get stuck in eddies, "gasping for breath," when deluges of rain water flowed down the creek.

"It gives one hope," Van Ness said. "…I've seen a real change in not just that people understand the message, but they want the information. Whenever you make a decision you have competing needs, and now streams are being considered at the table with the other needs. It's very exciting because it wasn't always that way."