About This Route
Hetch Hetchy Reservoir, at 3,900 feet in Yosemite's northwest, spans 1,800 acres behind O'Shaughnessy Dam; access via Evergreen Road (reservation required seasonally). Shore dives possible from Kirkwood Powerhouse trail, revealing submerged trees and granite walls to 40 feet. Cooler than lower Merced (50°F avg), viz variable from runoff. SFPUC manages; scuba allowed but no facilities, NPS oversight applies: buddy system, own risk. Less altitude issue but colder, deeper.
Safety Considerations
Moderate altitude; standard tables with adjustment. Strong inflows post-snowmelt create currents; check USGS gauges. Dam releases unpredictable; dive downstream cautious. Poison oak trails; tick checks. REI: drysuit must, lights for stumps. Coordinate with Hetch Hetchy Entrance (209-379-3087).
Essential Gear
7mm semi-dry, steel tanks, wreck reel for trees, dive knife.