BELLEVUE — The state, Port of Seattle and large cruise ship operators want public ideas on improving a 7-year-old environmental agreement for the big vessels.

Deadline for public comment is Nov. 22.

The 2004 memorandum of understanding bans cruise liner waste-water discharges in Washington state waters — including the Strait of Juan de Fuca — unless a ship’s onboard treatment system meets strict conditions, approved by the state Department of Ecology.

The discharge restrictions apply both to “blackwater” from toilets and “graywater” from other uses such as showers, sinks, laundry and kitchens.

Ecology, the Port of Seattle and the North West & Canada Cruise Association, which represents large cruise liners that operate between Seattle and Alaska from April to October annually, are asking for suggestions on amendments to their environmental protection agreement.

Proposed amendments must be sponsored by one of the three.

Sponsorship does not necessarily mean that the signatory will support adoption of the proposed amendment, Ecology says on its website at http://tinyurl.com/3qc9bu4, which provides details on criteria for amendments, information needed in each proposal and the complete memorandum of understanding.

The parties will consider any proposal sponsored by at least one of the three, and Ecology will request public comment on proposed amendments early next year.

The three involved in the agreement will decide on the proposals after a 30-day comment period.

Adoption of an amendment requires mutual approval by all three signatories.

In 2011, cruise ships made 195 calls at the Port of Seattle.