Once researchers learned to live-trap common mergansers and remove the host birds from lakes, swimmer's itch cases plummeted within three years. This was the experience on Lake Leelanau in the period 1999-2002. When reported cases again ramped up ten years later, the same method of removing the common mergansers was employed on North Lake Leelanau beginning in 2017. But this time, results were not conclusive. After removing all common mergansers for two years in a row, reported cases of swimmer's itch did not drop significantly. Ditto for Lime Lake and a number of others.