Emerald Lake is a glacial cirque lake in Yoho National Park, 8 km from Field. It is the gateway to the Burgess Shale fossil beds and home to Emerald Lake Lodge. The land is the traditional territory of the Ktunaxa, Secwépemc, and Stoney Nakoda Nations.

History. The lake was “discovered” for settlers in August 1882 by Tom Wilson, led by Stoney guide Edwin Hunter (Goldseeker), to the “Lake of Little Fishes”—but that lake is what we now call Lake Louise. Wilson named it Emerald Lake for its colour; in 1884 the name was reassigned to honour Princess Louise. Wilson later discovered a second brilliant green lake in the Yoho Valley and, finding the name available, recycled it. This lake inherited the recycled name—arguably the more visually deserving. The CPR recognized the lake’s allure and built Emerald Lake Lodge in 1902 as a wilderness satellite to Mount Stephen House. Before the Spiral Tunnels (1909), the “Big Hill” rail grade between Lake Louise and Field was a terrifying 4.5% descent; runaway trains were frequent. The tunnels reduced the grade to 2.2%, securing the line and allowing the CPR to market the “Swiss Alps of Canada,” flooding the lodge with guests.

Geology and colour. The lake sits in a classic glacial cirque carved into the shales and limestones of the Main Ranges during the Wisconsian Glaciation (~15,000–10,000 years ago). Its turquoise colour is rock flour—fine silt (0.5–2 microns) ground by glaciers on Mount Burgess and Mount President, carried in by meltwater and suspended in the water column. Microscopic particles scatter shorter wavelengths (blue-green) via Mie scattering; the calcium carbonate mineralogy of the surrounding peaks keeps the reflected light in the brilliant blue-green range. Colour varies seasonally: milky turquoise in June when melt peaks, deep translucent jade by August as silt settles.

Ecology. The western slopes of Yoho receive more Pacific moisture than the dry eastern Rockies. The steep, wet cliffs host “hanging gardens”—mosses, ferns, and rare orchids (Calypso Orchid, Yellow Lady’s Slipper) fed by mountain seepage. Mammals include Grizzly Bear and Moose; the shoreline is frequented by Moose seeking aquatic vegetation. Common Loons nest on the lake; Osprey dive for fish. Historically the lake held Bull Trout (species at risk) and Westslope Cutthroat Trout; the ecosystem has been altered by introduced Brook Trout.

Burgess Shale gateway. The lake is the trailhead for guided hikes to the Burgess Shale on Mount Field and Mount Burgess—where Charles Walcott discovered the fossils in 1909. The Walcott Quarry lies above the lake on Fossil Ridge.

Seasons. November–May: the lake freezes under ~2 m of ice and snow; cross-country skiers and snowshoers use the surface. Avalanches from the President Range remain active. June–July: break-up; the colour is most electric as fresh glacial melt brings peak rock flour. August–October: silt settles, the lake shifts to deep jade; hanging gardens bloom, loons rear chicks.

Conservation—Whirling Disease. In late 2023, Whirling Disease (Myxobolus cerebralis) was detected in Emerald Lake—the first confirmed case in British Columbia. The parasite attacks cartilage in young fish, causing the characteristic “whirling” behaviour and death. Parks Canada closed all waterbodies in Yoho National Park and Kootenay National Parks to personal watercraft and angling; the closure was scheduled to remain until March 31, 2026 to prevent spread to the Columbia River drainage. Boots, boats, and pets can inadvertently transport the parasite; the challenge is balancing visitation with protecting the watershed.