Take it from someone that raises trout to trophy size year around in a pond -- a bigger pond is rarely better when it comes to holding over trout in a pond year around. 3 acres won't work unless you have special conditions and lots of ground water flowing through as in hundreds of gallons per minute. If that's what you want I hope you have deep, deep, pockets and lots of ground water.
Here are four options for holding over trout in an earthen pond.
1.) Deep water in a sterile pond as in a gravel pit whose hypolimnion layer does not get oxygen starved in late summer under stratified conditions. That is, the bottom is primarily sand, gravel and stone with little or no sediments that rob the ponds hypolimnion layer of oxygen during decomposition. And the water is not fertile raining down dead and dying phytoplankton and zooplankton that use up oxygen. Also there should be a lack of significant macrophytes that die and decompose using oxygen.
Just because this layer stays cold until the fall turnover doesn't mean squat if oxygen levels are too low and the trout have to move up in the water column to lethal water temps to get oxygen. One exception is sterile marl bottom lakes, which I have in my area, that hold trout year around. Even some of them are marginal trout habitat some years.
2.) The above with an infusion of pure oxygen on the bottom most likely via LOX tank(s). Doubtful even then it would be effective on a 3 acre pond. Much smaller yes.
3.) Hypolimnetic aeration. The addition of air via diffusers with enough flow to add oxygen but not enough to break up stratification, which would totally negate the purpose. This can be tricky as Esshup commented on.
4.) A small pond with moderate well water flow that is easy to keep cool in the summer.
With the price you would pay to excavate a 3 acre pond you could probably have a well and a 1/10th acre pond. My 1/10th acre pond easily handles up to 500 lbs. of trout with the 45 gpm I flow through 24/7 eight months of the year.
Perhaps you think 1/10th acre isn't big enough and it's like fishing in a bathtub? Not so. My 88 by 59 feet pond (9 feet max depth) is just the right size for pleasant fishing with a flyrod, live bait, or pellets. If you want a more challenging trout plant brown trout. Easy to manage as it takes only a few days with a sump pump in bucket to pump it down to remove fish that can't be caught to start over etc.
Summer surface temps rarely exceed 64 F. and my brook trout do very well in the pond even with annoying iron levels in the well water. The water is exchanged about every 1.5 - 2 days in this 100,000 gallon pond.
Banks are steep to keep warming down.
Here's is a temp profile at 3 P.M. recently when air temps were in the 90's. Water temps drops eventually during the night to about 60 from top to bottom. I also only run a diffuser in the center bottom during night hours to keep warming down in the summer.
Surface 66.5
1 foot 62.5
2 feet 61.5
3 feet 60.9
4 feet 60.7
5 feet 60.6
6 feet 60.5
7 feet 60.4
A picture of the trout pond after ice out. Btw trout do fine under the ice with no pellet feed.
No issues with oxygen levels all the way to the bottom in the summer due to a combination of gravity aeration of the well water before it hits the pond and some Chara on the bottom adding oxygen.
Here are some of the fish from the pond in previous years.
Over fed 12 lb. plus brown trout. (I know better now.)
6 lb. plus brook trout:
Nine pound plus rainbow trout.
Another overfed trout:
Brook trout of about 4 lbs. with color enhanced with astaxanthin (5D09).
My twin with a nice hook jawed male brown of about 7 lbs.
These fish were harvested before they died of natural mortality so they may have grown larger although how much more I don't know.
So do you still need a 3 acre pond?
