• A stator in the third powerhouse at Grand Coulee.
  • The penstocks above the water at Hoover Dam
  • The top of Shasta Dam in California
  • An automated gate structure on a canal in Washington.
  • An aerial photo of the sunsetting at Ruedi Reservoir in Colorado.


Quagga and zebra mussels arrived in the United States from Europe in the 1980s and spread to many eastern waterways, rivers and lakes. Quagga mussels were discovered in Lake Mead, Lake Mojave, and Lake Havasu on the Colorado River in January 2007. Zebra mussels were confirmed to be present in San Justo Reservoir in California in January 2008.

These mussels spread in numerous ways, mainly by floating in the currents of the water body or by "hitching" a ride on a boat or other water vessels that are used in infested water and then transported to another water body.

Knowledge and experience in the eastern United States indicates that once introduced, the mussels are almost impossible to eradicate in water bodies and facilities comparable to Reclamation facilities. 

A key observation of quagga and zebra mussels in the western states is not all contemporary measures can be applied to other facilities; one size does not fit all. The observations show that mussels react differently at different facilities because of water temperature, chemistry content differences, and a host of other unknown factors.

Spread of these mussels will cause significant impacts and damage to operation and maintenance of water storage, water delivery and hydropower structures and systems; recreational use; and aquatic ecosystems.

Reclamation is concentrating on proactive measures to help reduce the post-introduction spread and impacts of the mussels to Reclamation facilities and structures, thereby lessening the need for time-consuming and most costly measures of eradication.

Early Detection

In 2009, in order to stay ahead of mussel infestations and to help guide preventative and mitigation measures, Reclamation began a monitoring and detection program for many of its reservoirs determined most at risk of mussel exposure and infestation.  The aim is to detect the earliest stages of mussel exposure or infestation at Reclamation reservoirs, so that response planning and budgeting for protective measures can be initiated. Potentially several years may be available for response actions to be taken prior to full infestation of facilities after microscopic mussel larvae are detected early in a reservoir. Early actions may also be taken to prevent the spread of mussels to other water bodies.

Reclamation, in partnership with western states and other agencies, is monitoring more than 200 water bodies, including approximately 160 Reclamation reservoirs.  Reclamation regional and area offices have selected target reservoirs based on:

  • The potential for a mussel infestation to complicate, impair, or significantly increase the cost to provide critical Reclamation mission activities.
  • The annual number of boats and other crafts or equipment that are moved into this reservoir from other locations.

Monthly water samples from each water body are subjected to multiple tests to determine whether microscopic mussel larvae are present.  This testing includes:

  • Cross-polarized light microscopy, to highlight microscopic mussel shells.
  • Scanning Electron Microscopy, to provide very high magnification images for taxonomic identification.
  • Polymerase Chain Reaction and gene sequencing tests, to confirm the presence of mussel DNA

Learn more about Quagga and Zebra Mussels and how Reclamation addressing their presence in the West.

Updated: July 2, 2013