Too many of any species anywhere can cause problems, of course. But that's infrequently the case with shark-infested waters - more often, the sharks are simply living in their natural habitats. (Meadows are rarely butterfly-infested, and dolphins seem incapable of infestation.)
Beyond doing a disservice to the feeding behaviors of these fish, shark-infested is yet another mark against a species with more than their fair share of public relations problems. Let sharks teem, abound, bustle or brim. Ban infest.