Crouching in shallow water is an instakill? Way to go, 343... Why bother adding such a long stretch of it, then?
The accidentally Forge-able underwater area in Reach led to some great times (such as Bluerunner's fantastic Underwater Invasion map), and I'd love to see a canvas that lets you do that again, performance be damned. (I can think of three great maps that took advantage of that to great effect.

But seriously, every single Nature-based Forge cqnvas having generic brown, grassy cliffs and water is annoying.