AUGUSTA – Maine officials are seeking federal approval to designate Casco Bay the state’s first no-discharge area that would make it illegal for boats and ships to dump their waste in the bay.

Gov. John Baldacci announced Monday that the state has requested the designation from the Environmental Protection Agency to eliminate waste discharges from the thousands of commercial and recreational vessels that use Casco Bay each year.

It could take the EPA up to six months to review the proposal, officials said.

“As one of the most productive and heavily used bays in Maine, Casco Bay warrants the best protection we can provide,” Baldacci said.

The designation would require the 700 ships that visit Portland Harbor each year to hold their partially treated waste until they are at least three miles off the coast, said Joe Payne, Casco Bay keeper.

It would also affect recreational boaters who have ignored marine sanitation laws and dumped sewage overboard within three miles of shore. There are now about 20 pump-out stations in Casco Bay, up from just one a decade ago, Payne said.

“We’re going to get a lot less pollution in the bay,” Payne said.

Casco Bay includes the port of Portland and more than 20 harbors. The proposal would also extend the no-discharge designation up the Fore, Presumpscot, Royal, Cousins, Harraseeket and New Meadows rivers.

The bay includes more than 229 square miles of marine habitat and 197,000 acres of shellfish harvesting beds. It also has the largest concentration of eelgrass in New England, which serves as an important habitat for commercial fish species.

“We cannot stand by and let preventable pollution threaten these resources,” the governor said.

Baldacci has also directed the Maine Department of Environmental Protection to make sure all remaining “straight pipes” – pipes that carry untreated sewage from homes into the bay – are disconnected. Straight pipes have been tolerated in the past under special circumstances on some islands, but are now illegal.

Baldacci said his goal is to open 5,000 additional acres to shellfish harvesting in the next five years.