They are very strong swimmers.I have a lake front piece of property on Shuswap Lk. I have seen 2 deer and 1 moose swim across this lake which is actually the mouth of the Thompson River. It's 2 miles across and places can get over 100 ft deep.Both deer made it safely the moose I don't know. He was about 300 yards away from shore and a jet boat with a water skier went by him. He turned and started swimming back to the other side 2 miles away. I don't think he made it it's just a guess though, I lost sight of him.