Mysterious Island Appears, Then Vanishes in Canadian Reservoir

A massive island seemingly popped up out of nowhere in a Canadian reservoir ... only to completely vanish weeks later.

The bizarre floating landmass was spotted in British Columbia's Williston Reservoir, where boaters noticed what looked like a full-blown island covered in trees drifting through the water.

And this thing was huge ... roughly the size of two NFL football fields. Satellite imagery from July 21 confirmed it was real and floating about 60 miles west of the W.A.C. Bennett Dam.

Then came the weird part ... by August 5, the island had disappeared from satellite images ... and the utility that manages the reservoir says it still doesn't know exactly where the island went.

A spokesperson told CBC it may not have sunk at all, suggesting the island could've simply drifted back toward shore or into a more sheltered part of the massive reservoir.

Officials also suggest unusually high water levels may have ripped the island loose from the shoreline ... before winds sent it drifting across the reservoir.