Go as deep as you can. "Too deep" is a function of safety (aforementioned slope) and pond size, subsurface soil/rock types, and your wallet.

The pond will only get shallower due to silt, sediment, and erosion over time. The deeper it starts out, the longer its lifetime.


"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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