Oakwood Bottoms Greentree Reservoir, located in Jackson County northeast of Grand Tower, Illinois, is part of the Shawnee National Forest. The site, which lies in the Mississippi River and Big Muddy River floodplains, was drained by a series of channels and intensively farmed until acquisition by the federal government as part of the national forest. The land came under federal ownership in the 1930s and has been managed since 1964. The reservoir site is flooded during the fall and drained before the onset of the growing season. Because the Big Muddy River levee prevents natural flooding of this site, flooding is accomplished by pumping well water. As a result of tight soils and little drainage relief, the area is primarily a wet forest.
In southwest Jackson County, the Big Muddy River and Mississippi River floodplains meet, offering habitat for more than 200 bird species that have visited the Oakwood Bottoms region of the Shawnee National Forest. Many important bird species of the state breed here. These include Yellow-crowned Night-Heron, Least Tern, Black-necked Stilt, King Rail, Fish Crow, Mississippi Kite, Louisiana Waterthrush and Prairie Warbler.
The site also attracts copious migratory birds, including, in a given year, 10,000 waterfowl, 1,000 or more shorebirds, 1,500 or more waders and more than 50,0000 neotropic songbirds.
This site was chosen as an IBA because it met the criteria for Waterfowl, Shorebirds, and breeding Yellow-crowned Night-heron.
Plant communities present are representatives of a wet-mesic floodplain forest.