The comment about sloths and swimming rang a bell. I recalled something from my mis-spent youth, hanging about libraries.
So, I dug into the Archives here (Yeah, we all have our own), and pulled out an old copy of The Land And Wildlife of South America, By Marston Bates and The Editors of Life, from the Life Nature Library, copyright 1964.
On Page 190 of this august tome, I note a full page color photograph of a swimming sloth. A good part of this sloth’s body is above the waterline - it appears that the sloth may well be more bouyant than a human. It may be my imagination, but I could swear the thing is smiling, too. The caption reads as follows:
“The Awkward Sloth, called the Nimble Peter by derisive Spaniards, never leaves the trees unless it absolutely has to. But when forced out by floods, it floats and flaps its way along. In fact it is almost impossible to drown a sloth. Totally immersed for 30 minutes, they will still revive - possibly because their slow metabolism rate requires less oxygen in their blood.”
IIRC, sloth regularly leave the trees, in a slow and laborious fashion, to defecate and bury their scat. (My goodness, I wonder if there’s a correct term for sloth poop. Fewmets? naaaah.) If they did not do so, it has been said, their slow rate of movement would allow predators to more easily spot them by the piles of dung under the sloth trees.
I currently do not have a reference for that, however.
So there you have it - The Sloth swims, albeit not as gracefully as other animals might.