Essentially, only the water where sunlight penetrates holds O2. Fish can go down there but can't live there. You can sometimes feel the cold water thermocline when treading water. Right now, my water level is down about 4 ft so I have lost a huge amount of the productive environment. Depending on how the pond is built(sloping sides, etc.) the top 25% can easily hold 40% or so of the water.

It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

Without a sense of urgency, Nothing ever gets done.

Boy, if I say "sic em", you'd better look for something to bite. Sam Shelley Rancher and Farmer Muleshoe Texas 1892-1985 RIP