The King County Major Lakes Monitoring Program relies on automated sampling equipment capable of collecting data at multiple lake depths at a sub-daily frequency. Two types of equipment are currently in use: thermistor chains (water temperature monitoring equipment) and profiling platforms. Descriptions of the equipment and data collection and management procedures are described below.Thermistor ChainsThermistor chains are composed of Onset HOBO Pro V2 water proof temperature data loggers (Model U22-001) set at fixed depth intervals along a polyethylene line. The manufacturer stated sensor accuracy is ±0.2 oC with a working range of 0 to 50 oC. Temperature resolution is 0.02 oC.The Lake Washington thermistor chain is attached to the southern floating span of the I-90 bridge near the center of the lake.Profiling PlatformThe Lake Washington profiler is located near the center of the lake and all data can be accessed from the the King County lake buoy web site (https://green2.kingcounty.gov/lake-buoy/default.aspx). The profiling system was manufactured by YSI Incorporated (now Xylem) and is equiped with a weather station (air temperature, relative humidity, wind speed/direction, and total solar radiation). The profiler is equipped with a YSI EDS6600 series sonde with sensors for temperature, dissolved oxygen, specific conductance, pH, turbidity and chlorophyll fluorescence. The profiler records data every 1 m to 55 m depth at least three times a day.