There are approximately 460 lakes in Snohomish County, most of which are very small or located in the Cascade Mountains and foothills. Approximately 60 lakes are located in the populated lowland portions of the county.
Since 1992, Snohomish County surface water management (SWM) has worked with citizen volunteers to monitor lake water quality in about 40 lowland lakes. Current and historical lake water quality data are available online in SWM's interactive Water Quality Database.
Snohomish County's State of the Lakes Report (2003) summarizes the results of SWM's lake monitoring performed from 1992 through 2002, as well as occasional monitoring from the mid-1970s. In addition, the report contains detailed monitoring summaries for 35 lakes. Annual update reports provide updated water quality monitoring information for each individual lake as new monitoring data are collected.