Grassy Slough Land and Water Reserve, owned by The Nature Conservancy, is near Belknap, Illinois, in the extreme sourthern part of the state. More than 2,000 restored acres in this preserve are enrolled in the Cache River Special Wetland Reserve Program. These wetlands are designated as Wetlands of International Importance by the Ramsar Convention of the United Nations Educational, Scientific and Cultural Organization.
Before TNC purchased this preserve, the land was planted annually with vegetable crops. Historically, this site was dominated by low, wet bottomland hardwood forest and swamps. Grassy Slough has long been considered an important tract for preservation because of its geographic location. The tract separates the Little Black Slough Unit of the Cache River State Natural Area from the Lower Cache River Unit of the Cache River State Natural Area. With registration of Grassy Slough, the results will be an unfragmented 16,778.5-acre riparian corridor in conservation ownership.
The Nature Conservancy and many other partners have sponsored an Annual Southern Illinois Birding Blitz at the end of April since 2001. In 2002, seven teams competed to see as many species as possible within 24 hours. Together, the teams recorded 176 species, including American Bittern, Henslow?s Sparrow, Virginia Rail and Bald Eagle. Breeding birds in this preserve include Yellow-throated and, Prothonotary Warblers, Brown Creeper, Pileated Woodpecker. Red-shouldered Hawk and Yellow-crowned Night-Heron. The restored wetlands here also attract migratory waterfowl and shorebirds, along with summering and post-breeding Great Blue Heron and Great Egret.
This site was chosen as an IBA because it met the criteria for the Short-eared Owl (winter) and Barn Owl.
Forest loss in the watershed due to logging and agriculture, especially along the lower stretch of the Cache, has been extensive. Efforts to dry out the region have resulted in modifications to the Cache that have severely affected its natural flow. These modifications have degraded the river and associated cypress and shrub swamps. Water quality of the river has suffered greatly, due in part to soil erosion from cleared land in the watershed. Up to 150 tons of soil per acre are washed into the river and wetlands each year.