I don't have any WTF, but my golden tree frog (fairly large frog), also likes to swim. I've got her in with a good 8" or so of water, and she loves to swim in it and submerge herself and all that. We shouldn't really be surprised that they like the water (lol), most frogs are, after all, born in a body of water. It's frogs that are born in tiny bits of water, like a dart frog, for example, that you really have to worry about drowning. Their legs just don't seem to be made for swimming! Most frogs swim just fine.

It is of course important to make sure you have plenty of places for them to get out easily in case they get distressed or stuck somewhere.