Rock Island Ecological Services Field Office

Midwest Region


Rock Island Field Office

1511 47th Avenue
Moline, IL 61265
Phone: 309-757-5800
Fax: 309-757-5807
TTY: 1-800-877-8339 (Federal Relay)




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Environmental Contaminants


Cedar River Mussel Biomonitoring (Iowa)


Causes for low mussel abundance in the Cedar River is the focus of a biomonitoring project being carried out by the U.S. Fish and Wildlife and the Iowa Department of Natural Resources.


Young black sandshell mussels.

Black sandshells (Ligumia recta) were once common in the Cedar River.  Natural resource managers hope to determine and eliminate the cause for low mussel abundance in the Cedar River so that mussels, like the black sandshell, can be reintroduced back into the former mussel bed locations.  The many fine threads in the photo are byssal threads put out by these young mussels to secure themselves to the substrate so that they do not get washed away during floods. 

Photograph by USFWS; Robert Pos

The Cedar River is a large river ecosystem in east central Iowa with rich cultural and natural histories that are threatened by development and human use.  Efforts to restore natural resources and balanced uses will contribute to a clean and safe environment, provide outdoor recreation, and preserve Iowa and American heritage.


Project Description

The Cedar River historically supported healthy and diverse numbers of freshwater mussels.  In fact, the Cedar River was chosen as a location to reintroduce the State and federally listed endangered Higgins eye pearlymussel as part of a recovery project for the species.  However, during follow up monitoring of the reintroduction work, no Higgins eye mussels could be found.  Surveys for other mussels also found that numbers seem to be down as indicated by the difficulty in finding live specimens.  The Iowa Department of Natural Resources and the U.S. Fish and Wildlife Service are concerned because of the importance of mussels in river ecosystems and because the decline in mussels indicates that the river likely has problems that have not been identified.  The mussel declines could be due to water quality problems.   Therefore, the Service’s Rock Island, IL Ecological Servcies Field Office has teamed with the Iowa Department of Natural Resources to conduct biomonitoring studies to determine whether problems with water quality have caused the mussel declines in the Cedar River, and if so, the exact nature of the water quality problems.  The results of the biomonitoring can be used by biologists to re-start stocking mussels back in areas of suitable habitat without water quality problems. 



Mussel silos

Immature freshwater mussels were placed in small concrete domes that sit on the river substrate referred to as mussel silos.  The mussel silo contains a hollow center which allows a chamber holding juvenile mussels to be placed inside.  Water flow over the silo creates a difference in current which pulls water through the chamber providing the mussels inside with oxygen and food.  The sentinel mussels can be moved to various locations to monitor their health and growth and help narrow in on any water quality problems. 


Mussels provide ecological services that benefit the public.  They filter water and contribute to the biological diversity in river ecosystems.  High biological diversity provides resilience that helps system rebound from natural and man-made impacts to rivers.  Mussels help stabilize river substrates and mussels beds actually act as a substrate, colonized by a variety of other aquatic invertebrate species.  These invertebrate species are in turn attractive to bait fish and game fish that feed on the bait fish.  Mussels are declining at an alarming rate with up to 1.2% of the North American species becoming extinct every decade(Ricciardi A. and J.B. Rasmussen. 1999. Conservation Biology, 13(5):1220-1222).



Map of Iowa that shows location of the Cedar and Iowa Rivers.

Map of the Cedar River and Iowa River drainages.  Iowa River is on the left and the Cedar River is on the right. 

Cedar River

The Cedar River runs from southern Minnesota to its’ confluence with the Iowa River in southeast Iowa flowing through the towns of Austin, MN, Cedar Falls, IA, Waterloo, IA and Cedar Rapids, IA.  Cedar Rapids experienced serious flood events from the Cedar River in 1993 and 2008.   The non-government conservation organization, American Rivers, is concerned about the structural proposals that may be offered to address flooding along the Cedar River and this is the reason that the Cedar River was named by American Rivers and “one of America’s most endangered.”  About 31% of the Cedar River in Iowa is listed as impaired due to bacteria contamination, nitrate exposure, and declining mussel populations.


Mussel Environmental History in the Cedar River


Mussel diversity and abundance are monitored during periodic surveys of Iowa's rivers.

Photo by Mike Coffey; USFWS

In 2000, the Iowa State University surveyed mussels in the Cedar River and compared the results to a similar study conducted in 1985.  The results indicated a decline in excess of 50% for the Cedar River mussel population.  As part of a follow up monitoring in 2005 after the release of Higgins eye into the Cedar River no Higgins eye pearly mussels were found.  In addition, the monitoring also indicated that only 43 live mussels of 9 species were found. Future restocking of Higgins eye pearlymussel was stopped because of the decline in the mussel community.  The Iowa Department of Natural Resources surveys mussels in many of their large rivers including the Cedar River.  Recently, it took State fishery biologists almost 38 minutes to find a live mussel at known mussel bed locations in the Cedar River compared to nearby rivers where it took between 3.2 to 5.9 minutes. 







Biomonitoring Protocol in Photos


Data from the 2011 Summer Biomonitoring



Links to More Information

River gage in Cedar Rapids, Iowa
Iowa Department of Natural Resources
Mussels of Iowa
Genoa, Wisconsin National Fish Hatchery
U.S. Army Corps of Engineers - Higgins eye Mussel Relocation Plan



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Last updated: April 24, 2015