The Greater Lake Koshkonong IBA encompasses all of Lake Koshkonong as well as adjacent and nearby habitats at Koshkonong State Wildlife Area, Red Cedar Lake State Natural Area, and Rose Lake State Natural Area. This area hosts a diversity of wetland habitats including shallow and deeper water submergent and emergent marshes, sedge meadow and wild rice, open water, streams, conifer swamp, and floodplain forest.
The wetlands, conifer swamps, floodplain forests, and open waters of the Greater Lake Koshkonong IBA include areas that have been monitored for bird life since the 1840s, with observations of exceptional diversity and abundance recorded by early Wisconsin naturalists Thure and Ludwig Kumlien (Matteson and Highsmith 2003; Robbins 1991). Lake Koshkonong continues to harbor large concentrations of waterfowl of over 20 species during both migratory periods. Recent surveys recorded over 20,000 ducks during spring migration, with especially large numbers of Ruddy Duck and other divers. The wetlands support herons and bitterns, Blue-winged Teal, Yellow-headed Blackbird, and significant numbers Black Tern and Marsh Wren. Sightings of American White Pelican have been increasing in recent years. Floodplain forests support Acadian Flycatcher, Eastern Wood-Pewee, and Prothonotary Warbler. Cerulean Warblers have been recorded in this area in the past.
Increased water levels, which some lakeshore residents desire in order to operate larger recreational boats on the lake, threaten the wetlands surrounding Lake Koshkonong. Many of the extensive wetlands originally found around the lake have disappeared with the onset of higher water levels after the installation of the Indianford dam in 1919. Additional increases in water levels would further decrease the area of emergent marshes and affect the hydrology of the floodplain forests. Invasive plants also threaten wetlands and upland habitats alike in this region. Existing woodlands are plagued by the encroachment of garlic mustard, while wetlands are affected by purple loosestrife and reed canary grass, among others. Much of the land on the west, south and east shores of Rose Lake is owned and managed by Jefferson County as Dorothy Carnes Park, and has also been designated as Rose Lake State Natural Area. Ongoing management here has cleared invasive plants from the woods on the west side and planted prairie, with more planting planned. Some local landowners and stakeholder groups, notably the Lake Koshkonong Wetland Association and several hunting clubs have a history of conservation and management in this area. Hunting clubs have existed around Lake Koshkonong since the late 1800?s; the Carcajou Shooting Club, incorporated in 1896, is one of the oldest hunting clubs in Wisconsin. Currently, most of the nearly 5,000 acres of wetlands immediately surrounding the lake are owned by hunting clubs. The commitment of these clubs to the preservation and improvement of habitat for waterfowl and upland game birds has been critical to maintaining wetland habitats for many other bird species. These organizations will continue to be active in habitat restoration, invasive species control, and public education and outreach.