To be fair, this is a hazard anywhere, at any time, and you should always be vigilant. In an old barn, we have what looks like an old log split in four to use as beams to support a loft floor, they've been there for 40 odd years, last year, I pulled a similar whole trunk out of the sea, in the north west highlands of Scotland. I saw a gull 'standing on the water' from a distance but in reality it was standing on a log that was wholly submerged, 18 inches diameter and 25 feet long
Because its the same wood, shape & size as the one in my loft, suggests it could have been a floater for years !!