Established in 1992 by Iroquois National Wildlife Refuge and Ducks Unlimited, Olsen Marsh honors Odmond "Odie" Olsen, who began at Iroquois National Wildlife Refuge as a maintenance worker in 1958, became its first biological technician, played an instrumental role in the refuge's early development, and retired in 1988 after 30 years of service. The 365-acre emergent marsh known as Cayuga Pool is a vital wetland that supports secretive birds such as the least bittern, Virginia rail, pied-billed grebe, and black tern, while the nearby twin marshes, Olsen North and Olsen South, along with surrounding grasslands, provide waterfowl, upland birds, mammals, and other wildlife with places to feed, rest, nest, and raise their young.