State and federal environmental officials Friday formally designated the waters surrounding Martha’s Vineyard and south of Cape Cod off limits for the discharging of boat effluent. The designation means that nearly 95 per cent of state waters around Massachusetts are closed to effluent discharge. State Energy and Environmental Affairs and U.S. Environmental Protection Agency officials made the announcement this morning at a gathering at Aselton Park in Hyannis.

From now on all boats, with a temporary exception for Steamship Authority ferries, are prohibited from discharging their sewage into these state waters. The designation of these waters, called the South Cape Cod and Islands No Discharge Zone, adds one more zone to the 16 distinct areas around the state that are closed.

“EPA is thrilled that Massachusetts has achieved this significant milestone in protecting coastal water quality and our local environment,” said Curt Spalding, regional administrator of EPA’s New England Office, at the Hyannis meeting. “There are few environments more special than the beaches and bays of Massachusetts, and now our citizens and visitors can rest assured that we are doing everything we can to protect these cherished environments.”

Nantucket was among the first areas in the Commonwealth to be designated a no discharge area and that was in 1992. The new no-discharge zone expands the closed waters around Nantucket to include all the state waters South of Cape Cod and include Martha’s Vineyard. The only exemption is the federal waters inside Nantucket Sound.

Also, by agreement, a narrow area traversed by Steamship Authority ferries is exempt for several years, until the authority can upgrade shoreside facilities and make modifications to all of its ferries that serve the two Islands. The Steamship Authority expects the conversion costs to be $3 million. Last year the authority received a $1.27 million state grant to cover the costs of the landside conversion. The process to get all parties onboard the designation, according to a release, took five years.

The new designation protects 26 miles of coastline and encompasses 733 square miles of state waters.

With this designation, discharges of treated and untreated boat sewage are prohibited within the town boundaries of Chilmark, West Tisbury, Tisbury, Oak Bluffs, Edgartown, Gosnold, Falmouth, Mashpee, Barnstable, Yarmouth, Dennis, Harwich, Chatham and Nantucket.

“With the help of our community leaders and federal partners, the dream of clean coastal waters up and down the Massachusetts coastline is now a reality, protecting our precious marine habitats and recreational areas for years to come,” according to Governor Deval Patrick.