I've swum a wide variety of frogs for my thesis work, and none ever failed to do so. Most were surprisingly good, even if you'd expect otherwise (red-banded walking frogs, chubby frogs), and all had more than enough capability to cross a 24" x 12" tray of water deep enough to prevent "wading" or anything like that.

If a frog died in the water, it's most likely due to another cause.