How deep is too deep?

I'm enlarging my pond, going from about 6' x 6' x 3' to
something like 10' x 15'. I thought I go 5' deep this time
but now I'm wondering if 7 or 8 feet is "too deep". Does anyone
have a pond this deep or deeper and do you regret it? Digging
will be more of a chore but you only have to do it once :-)

My philospohy is to pick a length and width that fits the
garden asthetically and then make it as deep as possible.

Thanks for any input.