Surface waters are permanent, open bodies of water 0.1 acre or larger. They are separated from wetlands by their permanence and by their general lack of emergent woody or graminoid vegetation. There are four subclasses: Lake Michigan, Reservoir, Impoundment, and Stream.

Lake Michigan

Only about 7% of Lake Michigan is within the State of Illinois' jurisdiction and only that portion which is in Illinois is included in this inventory.

Reservoirs

This classification includes only the three U. S. Army Corps of Engineers reservoirs (Carlyle, Rend and Shelbyville).

Impoundments

This classification includes all standing bodies of water (lakes and ponds) constructed by artificial means or formed by nature, except Lake Michigan and the three Corps of Engineers reservoirs. Impoundments are further divided into categories according to ownership as follows:

• State: This category includes all impoundments owned or leased by the Illinois Department of Natural Resources.
• Public: This category includes all impoundments owned or leased by a government agency, other than the Illinois Department of Natural Resources, that have public access.
• Organization: This category includes all impoundments owned or leased by any organization. Included are sportsmen's clubs, scouts, church, civic, fraternal, associations, homeowner groups, country clubs, industrial, institutions, etc.
• Commercial: This category includes all impoundments privately owned or leased for which a fee is charged for fishing. These areas are licensed by the Illinois Department of Natural Resources.
• Private: This category includes all impoundments privately owned or leased which are not operated as organizations or commercial areas.

Streams: This classification includes all flowing waters such as canals, creeks and rivers, regardless of ownership or leasing. Streams are further divided into four width categories as measured by their average width in a county. Intermittent streams are not included in the inventory.