Yes deer do swim on a regular basis. One of my favorite places to hunt isa funnel were the deer cross a small river, there's a large field to one side, a small wood lot and then a bluff, they cross the river all the time in their daily routine. A deer's hair is hollow inside and serve's as a floatation device. they will float without even kicking,I worked on the Ohio and Mississippi river's as a deckhand years ago seen huge deer swimming the river all of the time, sometimes they would get tired and just float along with the current.