Inland Waterway User Fee Act of 1981

Inland Waterway User Fee Act of 1981 - Directs the Secretary of the Army, in consultation with the Secretary of Transportation, to prescribe a system of user fees to be levied on commercial transportation on the inland waterway system pursuant to this Act. Sets forth criteria by which such fees shall be established.

Authorizes the Secretary of the Army to utilize various mechanisms as means to recover Federal costs from system users.

Specifies that such fees shall recover 100 percent of Federal operation and maintenance expenditures and an amount necessary to amortize capital expenditures for rehabilitation or replacement of existing structures completed after October 1, 1981. Directs that such fees shall be credited to the Inland Waterways Trust Fund.

Sets forth civil penalties for failure to pay user fees.

Lists, by project, the percentage of Federal expenditures for operation, maintenance, construction, and rehabilitation of inland waterway projects to be assigned to commercial waterway transportation. Specifies that costs assigned to commercial waterway transportation for the Mississippi River and tributaries project shall be 25 percent of total project costs.

Amends the Inland Waterways Revenue Act of 1978 to make amounts in the Trust Fund available for operation and maintenance expenditures for navigation on all inland and intracoastal waterways with an authorized depth of 14 feet or less used for commercial transportation.

Authorizes appropriations for the purposes of this Act.