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Environmental Health - Toxic Substances

Toxics Program Remediation Activities

Yolo Bypass Study

  • Feasibility Studies
  • Site Characterization
Location Yolo Bypass, CA (West of Sacramento, CA), Cache Creek, CA
  • Correlation of Optical Backscatter Data with Total Mercury Concentrations to Estimate Mercury Loads
  • Engineered Floodplain
  • Levees, Weirs
Contaminants Metals, Mercury; Loss of Habitat is also a Major Issue

The increasing urbanization of land and channelization of rivers in the San Francisco Bay area has resulted in a loss of floodplains that provided habitat for the abundant fish populations in the Bay. As fish habitat decreased and contamination from human activities increased, the number of fish in the once-thriving Bay has declined. CALFED, a consortium of state, federal, and local agencies, has undertaken a multiyear effort to not only restore the fish populations in the Bay, but to solve other ecological problems as well.

The Yolo Bypass is a 60-kilometer long, 24,000 hectares, leveed floodplain. The Bypass was originally designed in the early 1900s to divert the flood waters of the Sacramento River away from Sacramento, CA, and other communities, and into a broad floodplain. Most of the Bypass was completed by the early 1930s by the U.S. Army Corps of Engineers. This engineered floodplain is now the largest remaining floodplain in the Sacramento River watershed. The Bypass is important to the greater San Francisco Bay ecosystem because it more than doubles the shallow water habitat needed by many species of fish for spawning, and it provides key habitat for migrating waterfowl. This vital habitat is threatened by mercury contamination. Scientists have measured elevated mercury concentrations in flood waters in Cache Creek, the Yolo Bypass, and the Sacramento River Delta. Cache Creek watershed is the site of abandoned mercury mines and it discharges into the Bypass.

To help provide the scientific information to address the above issues, USGS scientists and their colleagues have undertaken two studies. First, the scientists are studying what forms of mercury are being transported into and through the Yolo Bypass and are developing methods to estimate the loads of mercury and methyl mercury that flow into the Yolo Bypass from Cache Creek. The information from this study will help resource mangers address issues of mercury bioavailability in the vital shallow-water fish and waterfowl habitat in the Bypass.

Second, the California Department of Water Resources and CALFED are investigating ways to use the Bypass to help restore the fisheries of the greater San Francisco Bay ecosystem. USGS scientists and their collaborators are studying the hydrodynamics and ecology of the San Francisco Bay, the Sacramento River, and the Yolo Bypass. These studies have shown that:

  • Increasing the connectivity between the Sacramento River and the Bypass could possibly allow the Bypass to be used as a corridor for migration to and from spawning areas in the upper parts of the Sacramento River watershed.
  • Maintaining a certain minimum level of flow through the Bypass is needed to assure water of sufficient quality to support fish during the critical spring and fall months when fish are attracted to the Bypass.
  • Increasing the acreage of the natural floodplain habitat (shallow water habitat) in the Bypass could result in increased fish populations.

The results from these studies are being considered by CALFED as part of its effort to increase the ecological health of the San Francisco Bay watershed, and to manage the competing uses of the Bypass (fishery, wildlife habitat, agricultural production, and flood control) in an ecologically sound and beneficial way.

More Information
Contact James Kuwabara, USGS, National Research Program, Menlo Park, CA,
Sommer, T., Harrell, B., Nobriga, M., Brown, R., Moyle, P., Kimmerer, W., and Schemel, L.,
California's Yolo Bypass--Evidence that flood control can be compatible with fisheries, wetlands, wildlife, and agriculture: Fisheries, vol. 26, no. 8, p. 6-16.

USGS Studies Related to Mercury Remediation

Mercury Information

San Francisco Bay Information

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