King County monitors the ecological health of lakes Union, Washington, and Sammamish in a variety of ways including collecting and analyzing water, plankton, and sediment samples. Data analyses from the Major Lakes Monitoring Program are presented on the pages listed below.

• Temperature Trends A discussion of long-term changes in lake temperatures.
• Phosphorus Trends Phosphorus levels over time in Lake Sammamish.
• Trophic State Indices TSI values for lakes Sammamish, Union, and Washington.