It's that time of year when oxygen starts getting depleted in the deeper water along with the water warming up. I don't know what your well flow is, but if your pond is 1 acre in size you probably don't have enough well flow to keep the water cool enough and oxygen levels up.

You aquatic vegatation may be exasberating (sp?)the situation during the night by using oxygen, and if it gets thick enough will help warm the water by creating shallower water.

The trout are coming up for higher oxygen levels but they are gettting stressed by the higher temps and the fact that the warmer temps can't hold as much oxygen. If the temps don't kill them the stress will indirectly by causing them to come down with disease and parasites that attack their weakend systems. White eyes, pop eye etc. are indicators of this.

When I had trout in a seasonal pond I had the same thing. I also have a friend in Ft. Wayne that has observed this later in the summer although he has a much smaller pond than you and he now pumps in more well water.

I hate to tell you this but it will probably only get worse. Sometime in August you will probably lose all your trout. You could get lucky and a few may survive. Be aware though just because they don't float doesn't mean some made it. Many trout will not float up and will decompose on the bottom.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.