Given that you're in the same region as I am I'm assuming this is a spring to fall use pond only? I don't think a 3 ft deep pond could survive the winters we have here?

Assuming you're planning to seine it out at the end of the growing season I'd make the whole thing 3 feet, or maybe have a slight taper up to 2 feet or so.

I'd be really gun-shy about one that shallow...even with aeration I would think that O2 concentrations could be an issue at times? Someone more knowledgeable than I will likely chime in there.

Dale

[Linked Image from i90.photobucket.com]

"When tempted to fight fire with fire, remember that the Fire Department usually uses water." - anonymous