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The Major Lakes Sediment Monitoring Program was begun in 1999 in Lakes Sammamish, Washington, and Union. An updated 10-year program was launched in 2007 to collect sediment quality information near storm drains, swimming beaches, and wildlife habitat areas. Additionally, a two-tiered sampling design allows for the assessment of long term trends in the deep main basins of the three major lakes.

To understand what effect chemicals in sediments may be having on aquatic life, chemical concentrations are compared to sediment quality guidelines. The Washington State Department of Ecology has not promulgated numeric freshwater sediment chemical standards, but has evaluated existing numeric sediment quality guidelines and proposed a new set of numeric guidelines, known as the floating percentile method, for use in Washington State freshwater sediments.

In addition to using the floating percentile-derived guidelines, a more widely used set of guidelines that were developed by Smith et al (1996) in the Great Lakes region in 1996 were also used. These Smith guidelines represent a good balance between sensitivity and efficiency and also include guidelines for organochlorine pesticides (DDT, dieldrin, etc.), which are not included among the floating point guidelines.

This sediment quality indicator is divided into three ratings: 1) adverse effects to aquatic organisms from chemical concentrations are unlikely; 2) adverse effects to aquatic organisms from chemical concentrations are uncertain; and 3) adverse effects to aquatic organisms from chemical concentration are probable. The three large lakes, Lake Washington, Union and Sammamish are weighted equally at 30 percent each for this indicator.

Status: A total of 60 stations have been sampled in Lakes Sammamish, Washington, and Union. Overall, most of the stations found to have chemical concentrations high enough to probably be causing adverse effects in aquatic organisms were located in Lake Union. Lake Sammamish sediment quality was the best of the three lakes, while Lake Washington sediment quality was mostly good except for a few localized areas. 

The 2004 Sediment Quality Evaluation in Lake Sammamish, Lake Union, and Lake Washington Report analyzes sediment data collected between 1999-2001 and is now available in pdf format.

For more information about the sediment monitoring program contact Dean Wilson.