To clarify the circumstances during which the Administrator of the Environmental Protection Agency and applicable States may require permits for discharges from certain vessels, and to require the Administrator to conduct a study of discharges incidental to the normal operation of vessels.

Prohibits the Administrator of the Environmental Protection Agency (EPA), or a state with an approved National Pollutant Discharge Elimination System (NPDES) permit program under the Federal Water Pollution Control Act, from requiring an NPDES permit for a covered vessel for the next two years for any discharge: (1) of effluent from properly functioning marine engines; (2) of laundry, shower, and galley sink wastes; or (3) that is incidental to the normal operation of a covered vessel. Defines "covered vessel" to mean a vessel that is less than 79 feet in length or a fishing vessel.

Requires the Administrator to evaluate the impacts of such discharges, excluding discharges: (1) from a vessel of the Armed Forces; (2) of sewage from a vessel, other than the discharge of graywater from a vessel operating on the Great Lakes; and (3) of ballast water.

Provides that such prohibition does not apply with respect to: (1) rubbish, trash, garbage, or other such materials discharged overboard; (2) other discharges when the vessel is operating in a capacity other than as a means of transportation; (3) ballast water discharges; or (4) any discharge that contributes to a violation of a water quality standard or poses an unacceptable risk to human health or the environment.