Well, Lake Cochrane is rather unusual for a South Dakota water body -- but similar to a lot of the smaller MN and WI natural lakes, I believe. Cochrane is a small (330 acres) natural lake (glacial origin) and has good water quality. In fact, it was one of 5 lakes to maintain fish communities during the dust bowl in the 30s. The unique thing about the lake is that the submergent, rooted vegetation goes out to about the 14 foot contour. As a result, more than half of the lake bottom is covered by plants, which Norm knows is very rare for a SD natural lake. Most of our natural lakes are shallow and windswept.
For decades, this lake has had an abundance of natural hybrids, mostly between bluegills and green sunfish (although there are a few pumpkinseeds in there, and once in a while a hybrid looks more like a pumpkinseed). This high incidence of natural hybridization often occurs in one of two situations, both of which function in Lake Cochrane. Sunfish apparently select mates through visual cues, and natural hybridization is more common in lakes with an overabundance of aquatic vegetation. Apparently, visual cues can be obscured in the dense vegetation. Secondly, natural hybridization is more likely when one species is abundant and the other is not. In the case of Lake Cochrane, there are plenty of bluegills, but the green sunfish abundance is pretty low.
