About This Route
Thousand Island Lake sits at 9,833 feet in the Ansel Adams Wilderness, just off the Pacific Crest Trail near Donohue Pass in California's Sierra Nevada. Accessible via the PCT from Tuolumne Meadows or Agnew Meadows trailheads, this alpine gem draws hikers for its crystal-clear waters surrounded by the Ritter Range. The PCT section from Tuolumne to the lake spans about 10 miles with 2,000 feet of elevation gain, offering stunning views of Banner Peak. Swimming here provides a refreshing reward after tough climbs, but high altitude and remote location demand respect. According to the National Park Service (NPS), alpine lakes like this see frequent rescues due to underestimating cold water immersion.
Safety Considerations
Cold water temperatures rarely exceed 50 degrees Fahrenheit, even in August, risking hypothermia within minutes. Follow Leave No Trace principles by swimming only in designated areas to avoid damaging fragile shorelines. Check Sierra Nevada snowpack reports from the California Department of Water Resources before heading out; rapid melt causes swift currents. Altitude sickness affects 25 percent of visitors above 9,000 feet per REI expert guidelines; acclimate gradually. Never swim alone, and inform your group of the buddy system. Flash floods from afternoon thunderstorms are common; monitor National Weather Service forecasts for Inyo County. Wildlife like black bears frequents the area, so store food properly per NPS protocols.
Essential Gear
Pack a personal flotation device (PFD) from brands like Stohlquist or NRS for unexpected fatigue. Neoprene booties or water shoes from Astral protect against rocky bottoms and prevent slips. A dry bag from Sea to Summit keeps clothes and electronics safe. Include a whistle, signaling mirror, and waterproof first aid kit with thermal blankets. Trekking poles double as stabilization aids during entry and exit.
Emergency Tips
In cold water shock, float on your back to conserve energy and yell for help. If hypothermic, remove wet clothes, wrap in dry layers, and hike to Shadow Lake ranger station if possible. Activate an inReach satellite communicator to contact Inyo County Search and Rescue. For altitude issues, descend 1,000 feet immediately and hydrate with electrolyte tabs.
This guide equips you for safe swims that enhance your PCT adventure. Always prioritize preparation over impulse dips.