I see several threads about pumping out water and draining ponds if necessary to dig our or find leaks.

But what do people do with the fish when they pump all the water or most of the water out?

In my case, I pumped the pond down so that the fish concentrated in the deepest part of the pond. Then used an excavator to make a temporary dam isolating that deep area from the area that we were working on. I threw a bottom diffusion aeration system in there "just in case".

Dug out the rest of the pond, making it deeper than the holding area. Broke the "dam", made sure all the fish made it to the new side of the pond, then worked on the old side.

Thanks that makes sense, how big was your pond and how much deeper did you dig?

My experience with renovating ponds is that the fishery has suffered from the ill effects over a long period of time. In those cases, the fishery doesn't have much value at all. I look at it two ways. "If we keep these fish, will the fishery return to any semblance of health?" And, "What would it cost to replace them?"

In 90%+ of renovations, it's better to eliminate the fish, do a complete renovation, then let it fill with water and re-start. Takes less time, costs less money because the contractor doesn't have to move any extra dirt to save the few hundred dollars worth of fish.

My fish went out into the fields below. I was ready to do a full redo though and am now happy I did. When I drained my 2.5 acre pond, I didn't see a single large fish, not even a grass carp. I believe otters may have killed them but it's a mystery to me.

I restocked the way I wanted and am now feeding and hoping to manage the populations. My catfish are growing like crazy in just 2 1/2 months. The bluegill are odd. Some look like they haven't grown much at all while some easily tripled in size.

Hello.

It depends how hard it is to get a permit.

Here it is difficult, I must protect my Yellow-perch.
A+

It was between 1/4 to 1/2 acre and when at full pool it's now slightly over an acre. Went from 3' deep in one part to 8' deep in the other to 21' deep when we were finished.

I agree with Bob about starting over with the fish population.

1) It's cheaper if you want to stock more fish. If you have adult fish, you have to stock adult fish or a lot more juvenile fish to make up for fish getting eaten.
2) You are starting with a known population to make the pond reach your goals.