The sides of the lake's caldera are suicidally steep, and lead straight down into the water in many places. This may be partly responsible for the lake's most famous resident, the Old Man of the Lake.
The Old Man is a stump, a length of hemlock trunk, which floats vertically in the lake. And has been for at least a hundred years. Originally, five feet of the stump projected up from the water, silvered with age. But tourists kept jumping on it, breaking off little bits, and now only two feet projects up from the water's surface. The rest of the Old Man, a long length of bark-less tree trunk, hangs straight down into the near-invisible water.
According to Mike Dash on the A Blast From the Past blog, an early ranger cut down several trees from the lake's flanks to make a raft. He found that when the trees slid down into the water, the angle of their descent was so steep that many of them came to rest bobbing vertically in the water. This may well be how the Old Man originally arrived in the lake: skidding down the steep slopes above.
No one knows why the Old Man hasn't just rotted. At the very least, you would think that underwater algae and microscopic creatures would have nibbled it down to nothing by now. Or enough to make it sink! But it seems that the submerged trunk is completely waterlogged, a process which can preserve logs for hundreds of years. (Many waterlogged trees lie at the bottom of Lake Washington, and are dredged up occasionally for cash.)
The Old Man drifts around the lake to a surprising extent, as a government survey in the 1930s discovered. The lake has no real current, but winds push the Old Man to and fro as the weather changes. And miraculously, the top of the log has retained enough buoyancy to act like a small sail, allowing the Old Man free range of the lake.
Crater Lake has no native fish, but in the olden days the Park Service stocked the lake. They want those fish gone now, which means that you may fish to your heart's content, no permit needed, no limit imposed. Cast away from the approved locations, into the nation's most beautiful and awe-inspiring lake, and keep an eye out for the Old Man!