I have a 40 Gallon stock tank, my Cayuga (who is a nice healthy weight/size) can get out just fine every time, but my Blue Swedish (a fatty!) will have to give it a couple of tries if the water level is low. She's never gotten stuck and can always give herself a "lift" with a flap of her wings, but sometimes just seems too lazy to want to do that. It's like a last resort. But as long as you have adult ducks and you keep the water level high they should be fine! Ducklings I wouldn't leave unattended at all, get them in and out of the pond supervised.