Great pictures. I have never seen a squirrel swim.
One time I was bass fishing in Lake Lanier near the mouth of Bald Ridge, and spotted something swimming in the middle of lake. When I went to investigate, it turned out to be a very exhausted grey squirrel that was just barely keeping his head above water.
I dipped it up with my net and deposited it on my casting platform, where it just sat, very still, making no attempt to get away from me. When I nosed up on a nearby beach, it turned and realized that that stuff was dry land, and he jumped off and scampered up the hill.
I have no idea how he ended up in the drink, but it was clear from his reactions that swimming lakes is somewhat less desirable than climbing trees and scampering through leaves to make a deer hunter think the buck of a lifetime is approaching from behind his stand.