[Gretin]

I think the wells just throw you back out of the lake if you fall in it when it's dry.

Anyway, I'm not exactly sure where you're talking about, but if I guess correctly, there should be a place about half way along the coastline on the far side of the bridge that you can jump up on with Munch from the water. If I remember correctly there's a sort of pipe and then behind it there's two switches for opening both sides of the bridge.
Hope this helps...