Quick rundown.. South Dakota pond, actually an old bentonite pond almost 5 acres around 40 feet deep (basically a big deep bowl) not much for structure. I had an approximately 25 acre dam that the flood gates broke on and was going dry. Caught only bass and put it in this bentonite pit. These bass have only been in there over 2 years, and most were 2 plus pounds. They did reproduce in there as I am seeing and catching small fish that we did not stock. These 2 plus pound fish are now getting smaller. What would be the best way to go about this?

Catching bluegills and putting in there?

Stocking minnows twice a year?

Removing the smaller bass and restock the big dam once fixed?

If it were me. And I'm still learning:

Add large adult forage fish. In the south we use bluegill, but you should use what works in your climate. Check local hatcherys. The sooner the better as your breeding season is short.

Do not stock small fish or minnows. The hatchery will try to sell you some. They will just become quick happy meals for the bass.

Add structure. This is easy. Sink stuff.

Find ways to enhance habitat. Things like gravel spawning beds.

You may need to cull some of the bass to let the forage fish get going.

The real smart move is to get help from a guru. It'll cost, but an expert can evaluate your water quality and develop a smart culling program. I'd email Bob Lusk and see if he knows anybody up there.

And be sure to read Pond Boss Magazine. Full of stuff that helps.

Ditto and feed the BG with a high protein (45%) and you will be amazed how fast it will turn around