About This Route
St. Mary Lake, Glacier National Park's second-largest body of water at 5,018 feet elevation, features dramatic walls near Wild Goose Island and depths over 200 feet. Access via boat from Rising Sun Boat Tours dock or private craft; combine with Sun Point Nature Trail for shore prep. This turquoise glacial lake hosts perch, lake trout, and unique thermohaline layers from meltwater inflows.
Safety Considerations
Water temps hover at 50°F; sudden immersion risks cold shock response, leading to drowning if unprepared, as noted in NPS cold-water advisories. Halocline effects from freshwater inflows alter buoyancy, mimicking iceberg dive challenges; compensate with extra weights. Strong afternoon winds from Gunsight Pass whip up 3-foot waves; dive mornings only. Rocky bottoms snag gear; watch for kokanee salmon schools reducing viz to 15 feet. Altitude demands multi-level dive profiles per AAUS standards. Secure park boat permit and check bear activity near Baring Falls trailhead.
Essential Gear
Required: Waterproof drysuit (Aqualung Polar X), twin tanks for redundancy, wrist-mounted dive light (Dive Rite CX2); reel and guideline for wall dives; GoPro in housing for documentation; emergency O2 kit. REI stresses 12.5L steel tanks for better trim in low-buoyancy freshwater.
Emergency Tips
For lost gas, share air and ascend to 15-foot safety stop; use boat horn or flares to alert vessels. Swim to Sun Point if adrift; rangers patrol via motorboat. Activate personal locator beacon; St. Mary Visitor Center has first aid, 5 miles away. Monitor for DCS with ginger ale hydration post-dive.
Pro tip: 2019 incident involved wind entrapment; always file float plan with outfitters. Follow Leave No Trace by removing all dive markers.