The Big Walnut IBA includes the Hoover Reservoir, Blendon Woods MetroPark, and the Big Walnut Creek corridor. The Hoover Nature Reserve (owned by Columbus City Parks and Recreation) functions as excellent Central Ohio shorebird habitat in late summer. The reservoir attracts waterfowl in the spring and fall.

The Big Walnut Creek runs along the boundary of till plain and a glaciated plateau to the east. Many streams have cut ravines down to this creek. Most of the ravines are largely wooded, and most of the creek still supports a fairly mature riparian forest. Most of the level uplands on either side have been developed as suburban housing. The Big Walnut floodplain to the south supports a fairly continuous riparian forest, with sizeable sycamores, cottonwoods, silver maples, and Ohio buckeyes.

The Big Walnut IBA connects Blendon Woods MetroPark and the riparian corridor. The “island’ of Blendon Woods and the Big Walnut corridor makes this IBA particularly attractive to migrant passerines. Most of Big Walnut, all the way to its junction with the Scioto River, still has an intact riparian strip, resulting from controlled floodplain development efforts by the Columbus Water Department and Gahanna’s conversion of nearly the entire riparian corridor into parks and conservation easements.

The unusual topography of the upper reservoir has created a series of marshes, swamps, and mudflats unusual for central Ohio. Consequently, this area acts as a magnet for birds that favor these habitats, both in migration and during the breeding season. Upland areas in public management (Hoover Dam Park and Blendon Woods MetroPark) have an interesting mix of oak-hickory and beech-maple woods bisected by many small ravines, which host species of birds typical of mixed mature woodlands. Both also include small areas of successional fields that produce old-field bird species uncommon in Franklin County: Yellow-breasted Chat, Eastern Towhee, Brown Thrasher, and Blue-winged Warbler. Priority birds along Big Walnut Creek and in Blendon Woods include American Black Duck, Yellow-billed Cuckoo, and Blue-winged Warbler. Priority species in Hoover Reservoir include Black-crowned Night-Heron, Osprey, Bald Eagle, American Coot, and Prothonotary Warbler. The shorebird diversity is very high, ranking it among the top five shorebird sites away from Lake Erie.