Research conducted in the 1980's and 1990's on Glen Lake and Lake Leelanau determined that the majority of swimmer's itch cases at that time were caused by a parasite that cycled between two hosts: the common merganser duck and a species of snail (Stagnicola emarginata) which is common to sandy-bottomed lakes in northern Michigan. If both hosts were present on a given lake it was virtually certain that swimmer's itch would be a problem. Researchers reasoned that removing the common merganser from lakes could offer a far more effective and less ecologically disruptive way of breaking the parasite life cycle (vis-a-vis using toxic copper sulfate to destroy snails, et al.)