A floating mass of trees and driftwood roughly the size of two NFL football fields drifted loose on one of Canada's largest reservoirs this summer, vanished from satellite view for two weeks, and then turned up again nearly 20 miles from where it started — delighting satellite-watchers and mildly bemusing the utility that runs the lake.
The island was first confirmed in satellite imagery from July 20 on the Williston Reservoir, a vast hydroelectric lake behind the W.A.C. Bennett Dam in northern British Columbia, near the town of Mackenzie. At roughly 70 by 140 meters — about 9,800 square meters, or 105,000 square feet — the tangle of vegetation was substantial enough to show up clearly from orbit, floating free in open water.
A Reservoir at Record Height
BC Hydro spokesperson Bob Gammer told reporters the utility's working theory is mundane rather than mysterious: driftwood has been piling up along the reservoir's shoreline for years, slowly forming a raft dense enough for plants and even small trees to take root on top of the decomposing wood. This year, a heavy winter snowpack and steady summer rain pushed the reservoir to its highest water level in 14 years, and officials believe rising water and wind eventually tore the whole mat loose.
By mid-August the island had dropped out of satellite view entirely. "The most recent satellite images from two weeks ago showed no sign of the floating island," Gammer said, adding that it may simply have "slipped into a sheltered inlet" out of camera range.
It hadn't gone far. According to follow-up satellite tracking reported by CBC News, the floating forest resurfaced about 19 miles (30 kilometers) to the northwest, coming to rest along the shoreline of the reservoir's Ospika Reach, where the Ospika River feeds in. BC Hydro says the mass poses no threat to the dam or to boat traffic and is simply being left to drift, though the utility is continuing to monitor it by satellite in case it moves again.
Williston Reservoir, created in the 1960s when the Peace River was dammed, is one of the largest reservoirs in North America by surface area, and its shoreline has shed floating debris mats before — just rarely one large enough, or long-lived enough, to earn its own tracking updates.