The U.S. Coast Guard issued a Notice stating that, even though the United States is not party to Annex IV of MARPOL 73/78 (which comes into force on September 27, 2003), the Coast Guard will issue documents to qualifying U.S. flag vessels certifying equivalent compliance. Annex IV is the international sewage pollution prevention program. Vessels subject to MARPOL 73/78 without certificates demonstrating compliance may be subject to port state control measures
once the annex comes into effect. The annex comes into effect for new vessels as of September 27, 2003. For existing vessels, it comes into effect on September 27, 2008.
Source: Holland & Knight