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King County improving water quality by studying Issaquah Creek bacteria sources


Rainy weather detective work helps locate sources of fecal coliform bacteria pollution in Issaquah Creek.


King County Stormwater Servicesissy_creek_2016_web engineers and scientists in bright orange vests and official vehicles will be working in the public right of way to map the stormwater system and collect water samples to find and identify sources of bacteria pollution in the Issaquah Creek watershed.

Mapping staff will be in the area through 2017 and the sampling work by water quality field staff will be timed for rainy days when runoff can be collected.

High levels of fecal coliform bacteria in Issaquah Creek can threaten the health of the stream, and the health of the fish and wildlife living in the stream or drinking from it, and the people who enjoy its waters.

The creek and many smaller feeder streams flow through neighborhoods and is home to chinook, coho and sockeye salmon.

King County Stormwater Services employees are responsible for preventing pollution in waterways like Issaquah Creek. They are currently investigating possible sources of the bacteria by sampling Issaquah Creek and the roadside ditches that flow into the creek; identifying and tracing bacteria sources; and reducing or eliminating those sources.

Field crew members won’t enter private property without notification and the landowner’s permission.

Based on studies of streams with similar pollution, the main cause for higher fecal coliform bacteria levels have been human sources – and it’s likely that humans are the reason for Issaquah Creek’s high levels as well.

While waterfowl and wild animals also contribute fecal coliform bacteria in lakes and ponds, high bacteria levels in streams and creeks are often from humans, livestock, and domestic animals.

Water samples collected from the Issaquah Creek watershed will be used to grow bacteria in Petri dishes for 48 hours and scientists count the bacteria colonies to give an early estimate of contamination.

This helps quickly target areas with poor water quality, and is a fast and inexpensive way to identify bacteria hot spots to target for costly DNA testing.

The DNA technique has been used to help identify if the fecal coliform sources are human, livestock, pets or wildlife, and eliminating those sources in other watersheds, including the Bear-Evans and Boise creek watersheds.

Call 206-477-4811 if you see drainage or water quality problems. This is a clean water service from King County’s Stormwater Services.

For livestock owners, find more information and technical assistance about maintaining water quality at

For residents with a septic system, visit