The Door Peninsula has more shoreline and rare plants and animals than any other county in Wisconsin. Ancient rivers carved valleys through the peninsula’s soft limestone, and during the last Ice Age massive glaciers scoured out Green Bay and widened those valleys, creating rich and varied environments. Today those ancient river valleys are marked by wetlands stretching across Door County. One of the most valuable is the Mink River Estuary, which extends from Ellison Bay to Rowleys Bay across the peninsula. There, river and Lake Michigan waters blend in one of the country’s most pristine freshwater estuaries, an important fish spawning and bird migration area that supports several rare plants and animals.