Walt that was in AL. and is described as a phosphate pit and a limestone quarry. Phosphate = very fertile water in the south when limestone is present. Most of the Northern pits (Dave's reference) are not like that and they have low water fertility (rock , gravel and granite pits). There are only a small % of pits in the US that have limestone and phosphate together with good water (Fla has a bunch). IMO the difference is in the water fertility primarily and to a lesser extent the reduced competition for BG food (LMB crowded) not so much because of steep banks (little BG spawning area). In a LMB crowded pond the BG fry/sub adults are almost totally eaten whether BG spawning is high or very low. The biggest predator of BG fry are other larger BG by a wide margin. They in turn are eaten by the LMB.

Now if Bruce feeds and fertilizes he may have a pit that is close to those you mention as Dave suggests. That will be interesting because while he may have similar water conditions he may not have the growing season length but could have a life span advantage. Interesting to see how this unfolds.