To protect human health, the U.S. Environmental Protection Agency (EPA) is proposing more stringent exhaust emission standards for the largest marine diesel engines. These engines are used for propulsion on marine commercial vessels (called Category 3 engines) sailing in US coastal waters out to 200 nautical miles (the “Emission Control Area” or “ECA”).EPA’s proposal will also apply to C3 vessels operating in the Great Lakes (some ships, called Lakers, operate exclusively in the Great Lakes). These proposed Clean Air Act standards are part of a coordinated U.S.–Canada strategy to address emissions from the largest commercial marine vessels that affect North America’s air quality. EPA has previously regulated smaller marine engines found mainly in coastal and inland waterways, such as tugboats, push boats, fishing boats, ferries, etc.