For a few weeks this summer, part of British Columbia appeared to have come loose. A huge, tree-covered mass was spotted drifting across Williston Reservoir in northern British Columbia, looking less like a piece of floating vegetation than an actual island that had somehow slipped its moorings.
The formation was estimated at roughly 70 meters by 140 meters – about 9,800 square meters, or more than two NFL football fields. Trees and other vegetation were still growing on top of it, making the sight particularly surreal from the water. And then, just as strangely, it disappeared.
The first reports came from local boaters earlier in August, and photographs and video quickly spread online. B.C. Hydro, the utility that operates the reservoir, initially had trouble locating the object and was understandably cautious about accepting images at face value in an era of increasingly convincing AI-generated photographs.
Satellite imagery eventually settled that question. B.C. Hydro confirmed that the floating mass was visible in imagery from July 21. By August 5, however, it was no longer visible in the same area. Officials have continued monitoring the reservoir for signs that it has resurfaced elsewhere.
The disappearance does not necessarily mean the island sank. B.C. Hydro spokesperson Bob Gammer told CBC that the mass could simply have drifted into a sheltered area along the shoreline, where it would be much harder to spot from satellite imagery.
The utility also has a plausible explanation for how it got there in the first place. And it has nothing to do with anything supernatural.
How Does an Island Float?
The easiest way to understand the phenomenon is to stop thinking of the object as a conventional island.
It was probably not a solid chunk of land floating intact on the reservoir. Instead, B.C. Hydro suspects it developed over years along the shoreline, where driftwood and other organic material accumulated and decomposed.
Plants and trees then established themselves in the growing mass, their roots weaving through the organic material and helping hold everything together. Eventually, unusually high water levels may have done the rest.
Williston Reservoir reached its highest levels in about 14 years this summer after a winter of heavy snow and steady summer rainfall. B.C. Hydro opened spillways at the W.A.C. Bennett Dam in June and July as the reservoir filled.
The rising water may have lifted or undercut a section of shoreline vegetation and debris until the mass finally broke free. Once detached, wind and waves could push it across the reservoir.
That is the part that looks impossible from shore: a forest apparently moving across open water. But nature has been producing versions of this phenomenon for a very long time.
The Science Behind a “Floating Island”
Floating islands are usually made from some combination of peat, roots, decomposing vegetation, soil and waterlogged organic material.
In some environments, the plant material itself creates a buoyant mat. As vegetation grows, roots and stems become densely interwoven, while partially decomposed organic matter accumulates underneath.
Decomposition can also generate gases within the organic layer, contributing to buoyancy. Scientific studies of free-floating peatlands have documented mats capable of supporting substantial vegetation while remaining afloat.
That means a floating island does not need to behave like a piece of rock. It behaves more like an enormous natural raft. The trees on top can continue growing because the upper part of the structure provides a relatively stable growing surface, while the tangled root network helps bind the entire mass together.
Wind can then act on the vegetation like a sail, while currents and waves move the underlying mat. Eventually, however, the same forces that set an island free can destroy it. Strong winds and waves can tear the mat apart.
Collisions with rocky shorelines can break it into smaller pieces. If the organic structure becomes saturated or loses enough of its internal buoyancy, sections can sink. So an island can appear to vanish without actually disappearing in the way a solid island would.
It may simply have broken apart, moved into a sheltered inlet or gradually sunk beneath the surface. In Williston Reservoir, nobody yet knows which of those things happened.
This Has Happened Before
British Columbia’s wandering island is unusual, but it is not unique. One of the best-known examples is in Wisconsin’s Chippewa Flowage, where large floating bogs have become a local feature of the reservoir.
The most famous is the aptly named Forty Acre Bog, a huge floating mass capable of supporting mature trees. Local accounts describe floating bogs ranging from relatively small patches to several acres in size, with some moving substantial distances when high water and strong winds combine.
One particularly large bog remained in roughly the same location for decades before high water and wind pushed it across the lake and eventually broke it into smaller pieces.
The explanation there is particularly interesting because the landscape was transformed when the reservoir was created in the 1920s.
Much of the flooded land consisted of swamp and peat bog. Some of that organic material rose to the surface, where vegetation gradually colonized it.
What looks like an island is therefore sometimes less like a piece of land that learned to float and more like a piece of wetland that never quite stopped floating.
Similar free-floating peatlands have been documented in Europe and elsewhere around the world. Scientists studying a famous floating peat island at Lake Posta Fibreno in Italy, for example, have described a thick organic mat capable of remaining free-floating for centuries.
Why Williston Reservoir Produced Such a Spectacle
The unusual part of the British Columbia event may not be the existence of floating vegetation itself, but its scale and timing.
Williston Reservoir is enormous. Created behind the W.A.C. Bennett Dam in 1968, it is one of the world’s largest reservoirs by volume and covers roughly 1,760 square kilometers.
That makes monitoring every corner of it from the water impractical. B.C. Hydro relies partly on satellite imagery and reports from people living, boating and working around the reservoir.
This year’s exceptionally high water appears to have changed the shoreline dramatically. Local residents have reported more trees and other debris being pulled into the reservoir, while previously exposed shoreline areas have been inundated. For boaters, that creates a much more practical concern than the mystery of the wandering island.
Floating and partially submerged trees can be extremely difficult to see when the water becomes choppy, and hitting one at speed can cause serious damage to a boat.
The giant island may have captured the world’s attention because it looked impossible. But the landscape around it was behaving according to some very ordinary rules of physics.
Water levels rose. A shoreline mass became buoyant. Roots and organic material held it together. Wind and currents moved it.
And somewhere in the vastness of Williston Reservoir, the island is now either hiding, breaking apart or sitting beneath the surface. For the moment, even B.C. Hydro doesn’t know which.
Sources
- CBC News, “An island mysteriously appeared – then disappeared on B.C.’s largest reservoir,” August 2026.
- UPI, “Mysterious island appears and disappears in British Columbia reservoir,” August 31, 2026.
- B.C. Hydro, satellite imagery and information cited by Canadian media concerning the floating formation and Williston Reservoir.
- Scientific Reports, research on free-floating peat islands and their buoyancy mechanisms.
- Chippewa Flowage Lake Association, background on the floating bogs and the “Forty Acre Bog” in Wisconsin.
- U.S. Geological/academic and environmental literature on floating vegetation and peatland formation.
