Traveling around Ohio in search of wetlands, you soon discover that the majority of Ohio wetlands are confined to the western and northern areas of the state. This is reflective of the glaciated terrain of these regions of Ohio. Continental glaciers at one time covered almost two-thirds of Ohio and, upon retreating, left a random mass of gravels, clays, and soils dotted with numerous bogs, fens, marshes, and kettlehole lakes.

Some wetlands do exist in the broader valleys of southeastern Ohio and are also products of continental glaciations, but in an indirect sense. Many of the wetlands we find in southeastern Ohio are referred to as Teays Valley Wetlands. Approximately two million years ago, the Teays River was a large preglacial river and was the major stream system in Ohio. Then, as the southward advancing glacier blocked and dammed the northward flowing Teays River, a number of long, narrow lakes formed throughout southeastern Ohio. As the glaciers melted, large deposits of silts and clays washed into these lakes and developed into permanent wetlands with a unique assemblage of plants and animals.

A number of terms have been used over the years to describe different types of wetlands. Marshes are known by most as herbaceous plant wetlands. A marsh with significant standing water is often called a deepwater marsh, whereas a marsh with shallow standing water is referred to as a sedge meadow or a wet meadow. A swamp has woody vegetation, either shrubs or trees. Bogs and fens are peat-accumulating wetlands.

Nearly 95% of Ohio's historic wetlands have already been lost and most of the remainder have suffered some impacts. The Ohio Chapter currently protects and manages ten wetlands in the state, with links to each below. These wetlands are ecologically irreplaceable resources. Some of the preserves are open to the public. For others, visitation is limited to volunteer work projects, staff-led field trips and special permit.