One of the unusual characteristics of Upper Bear Creek is that it is home to one of the last remaining large populations of Western pearlshell mussels (Margaritifera falcata) in the Pacific Northwest. This family is in a near threatened status (two steps away from endangered). Since 1990, this species population has declined 17% in watershed regions.  A cause for more alarm, is the number of locations that the mussels can safely spawn. In Montana, a study was done in 2015 that shows by 2020, 25% of streams where these creatures are currently living, will no longer be suitable for them to survive in.

Western Pearlshell mussels are naturally camoflaged to look like rocks in streams and lakes. They usually appear as vertically implanted black shells with breather holes that close if disturbed, or they may be found lying horizontally on top of the substrate. Open shells indicate a dead mussel. Adult colonies are found in the main channels of streams, but often migrate to protected areas around logs and large rocks. Juvenile mussels live in the shoreline area.

Freshwater mussels have important functions in stream health. They filter impurities as they ingest food and provide nutrients for other stream creatures. They can live in compact colonies, which stabilize streambeds, and they are an indicator species for the health of the stream because pollution and siltation will kill them.

The life cycle is dependant upon a fish host (usually a salmonid), in which larvae, called glochidia, released by the mussels, attaches to the gills of migrating fish. This method gives them free transport to other areas. In a short time the glochidia drop off the fish and implant in the shoreline areas, later moving to the stream channels as adults.

Margaritifera falcata can live for more than 100 years. They are known to have been a part of Western regional streams for at least 2000 years. Archeological sites indicate they were a food source of indigenous tribes, which left mussel shell “middens” or piles of shells, at campsites.

According to the U.S. Fisheries & Wildlife Service there are about 300 species of freshwater mussels in the United States, of which 70% are extinct or endangered due to may factors associated with urbanization. Seven species inhabit areas west of the Rockies, with only three of those species being found in Western Washington. Margaritifera falcata is one of the most common of these species still found in Western streams, although it also appears to be disappearing rapidly due to urbanization.

Photos of freshwater mussels taken in September at the Northwest Stream Center in Everett by John Reinke, a long time Water Tender.

If you see freshwater mussels, it is very important not to disturb them in any way. Instead please note the location using the GPS of your phone and email the location and a picture to This information will be used to help conservation efforts. Information on both living and dead mussels are incredibly useful.

In 2012, Water Tenders paid another nonprofit organization (EarthCorps in north Seattle) to remove invasive yellow iris(a plant) from Bear Creek, in the area just north of the Woodinville-Duvall Road.  The property from which the yellow iris were removed belonged to a longtime Water Tenders member named Wendy who died earlier in 2017.

As part of the process, the team first investigated whether there were any mussels which might be disturbed by the iris removal process.  These were carefully removed and temporarily put in a segregated part of the stream for later replacement.
The photos show some of the uprooted mussels in the hands of the team leader.  His name was Hadi, and he was from Uganda.  (Many of the EarthCorps Volunteers are from overseas.)


Blevins, E., Jepsen, S., Brim Box, J. & Nez, D. 2016. Margaritifera falcata. The IUCN Red List of Threatened Species 2016: e.T91109639A91109660. Downloaded on 19 March 2017.