The lake occupies the site of the former town of Moncton, which was abandoned in 1915 after the reservoir flooded the valley.
Subsurface water movement causes the lake level to drop substantially during late summer and autumn.
Rattlesnake Lake is an artificial reservoir created as part of the Seattle water supply system.
The park contains remnants of old-growth forest, including large Douglas fir and Western hemlock trees.
The water is renowned for its cold temperatures even during the peak of summer.
Rattlesnake Lake is a reservoir located at the base of the Rattlesnake Ledge rock formation in the Cedar River Watershed. The lake is situated within a 111-acre park managed by Seattle Public Utilities. It is a popular destination for freshwater swimming, fishing, and picnicking. The water levels fluctuate significantly throughout the year due to the underlying porous glacial deposits that allow water to seep into the Cedar River. This unique geology creates a surreal landscape of exposed tree stumps during periods of low water. The lake serves as the trailhead for the popular, heavily trafficked hike up to Rattlesnake Ledge.
The shoreline during low-water season, where the stark, bleached tree stumps create a unique foreground against the mountain backdrop.
Bring water shoes to navigate the rocky, stumpy shoreline comfortably.
Check local water quality reports before swimming, as occasional harmful algal blooms can occur.
Arrive early on weekends to secure parking, as the lots fill rapidly.
Do not attempt to swim to the middle of the lake, as hidden submerged logs and unpredictable currents pose safety risks.
Park gates are locked nightly; specific hours vary by season.
Pack out all trash, keep dogs leashed at all times, and avoid climbing on the fragile exposed tree stumps.
