I doubt that the coal burning is the whole issue. Like CG said it is naturally occurring and that can account for 1/3 of what they find. If the coal issue was the only issue then it would seem Oologah would not be on the lowest level list, there's a power plant that uses coal right next to it. It seems that a lot of the larger lakes are safer probably due in part to the larger pool of water to dilute the toxins with and the fact that there is a lot of new water in old water out action.
CG do carp not eat the zoo-plankton? According to that article (again its Tulsa World, so it's investigation may be lacking) the zoo-plankton are absorbing the mercury and that's how it's introduced up into the food-stream.