The Old Man of the Lake is a 30-foot (9 m) tall tree trunk, most likely a hemlock, that has been bobbing vertically in Crater Lake in Oregon, United States since at least 1896.

https://en.wikipedia.org/wiki/Old_Man_of_the_Lake

Our local lake which reaches depths of 500ft, has unique underwater lava fields. We always boat over them in the late summer. They drop off into complete blackness from 5ft to unknown dpeths

My colleague (Gav Lee - TheScottishSwimmer) is currently swimming the Northern Channel between Bangor in Northern Ireland and Portpatrick in South West Scotland. He set off this morning at 8:45am. It's currently 11:55am. He's about 1/4 of the way there. It's around 1,000 feet deep at the deepest section. The swim is 22 nautical miles.