LAMOINE – The state has reopened 6,300 acres of fishing grounds around the south end of Mount Desert Island, including some areas that have been closed to shellfish harvesting for more than two decades.

It is the largest reopening of fishing territory in Down East Maine in recent history, made possible because state water quality experts walked the shorelines of MDI to find sewage discharges and get them cleaned up.

Fishermen have returned to the area, but the impact of the reopening this summer was blunted by frequent red tide warnings, officials said.

By the time the red tide season passed, just recently, many fishermen had changed focus from clams and mussels to scallops or lobster.

“I have a lot of problems with state government, but how they have managed shellfish is not one of them,” lobsterman Andy Mays of Southwest Harbor said Thursday.

“From the perspective of [clammers], the state has done a fantastic job going out and pounding the beaches and finding these pipes and cleaning them up so they can open more flats,” said Mays, who also works as the town’s shellfish warden.

State marine experts continue the painstaking process of finding and inventorying pollution sources around the island, most from residential homes that are licensed to discharge their wastewater into the Atlantic.

The Maine Department of Marine Resources is working statewide to identify discharge sources and reopen as much water to fishing as possible, according to DMR water quality specialist John Fendl.

Maine’s shellfish industry adds $45 million to the state economy each year. There are 1,600 licensed commercial dealers, according to the DMR.

The waters off Southwest Harbor and Mount Desert all the way to the Cranberry Isles to the south have been under a blanket closure since the mid-1980s because of the sheer volume of discharges and lack of an inventory to know exactly where the pollution was coming from, Fendl said.

Although the state Department of Marine Resources continually monitors water quality along the Maine coast for bacteria and viruses from human and animal waste, officials don’t expect to reopen any other large areas at this time, Fendl said.

“We’ve been re-evaluating some [pollution] sources,” he said of the MDI area, “and with today’s technology we can be more exact” and therefore reduce the area that needs to be closed down around discharge points.

Most of the 6,317 reopened acres stretch roughly from King’s Point in Southwest Harbor to Ingraham Point in Mount Desert and south to the Cranberry Isles.

Several zones around Great and Little Cranberry islands, while relatively small, are still off-limits for fishermen, Fendl said. And shellfish harvesting is limited around Sutton Island.

But the deep water around the Cranberries is now open for harvesting mussels, clams, oysters and quahogs, Fendl said.

The areas that will remain off-limits to fishermen, some permanently, are places where the state has approved overboard discharges from homes, businesses and municipal plants.

For example, a swath of Frenchman Bay on the eastern side of Bar Harbor from the downtown to Hulls Cove will likely always be closed to shellfish harvesting because that’s the area where the town discharges its treated wastewater.

According to Fendl, the chlorine used in sewage treatment processes can kill bacteria, but some types of viruses survive the process and end up in the ocean.

Fendl said the state assumes the worst in deciding how much acreage to close around each discharge site because systems fail without notice and when they do, raw sewage is dumped into the water.

“Nothing’s perfect, but we do a good job. We probably get 95 percent of the pollution sources out there,” he said.

Lobstering and saltwater fishing are unaffected by the fishing bans because they are not “filter feeders” like shellfish, Fendl explained.

Mussels, clams, oysters and quahogs have natural filters in their bodies that catch and retain contamination, so that anyone who consumes the shellfish is at risk of potentially serious illness, according to officials.

There are 87 water sample stations on MDI and 1,000 in all in the eastern district, which is headquartered at the Lamoine State Park and bounded by the Penobscot River. It extends from Stockton Springs to Calais.

The western division, run by the marine resources office in Boothbay Harbor, covers the southern half of the coast and west to the New Hampshire border with 1,500 water sample stations.

Mays, Southwest Harbor’s shellfish warden, said fishing in the newly-opened water has been spotty because of the red tide warnings this summer.

Red tide is a term that describes seawater discolored by red algae that poisons marine life. It is prevalent along the coast during the summer and can be deadly to people eating fish from contaminated areas.

The red tide season has passed for this year, Mays said.

When Acadia National Park installed a new sewage treatment system at popular Seawall Campground in Southwest Harbor this year, it was able to abandon a decades-long practice of discharging treated wastewater into the ocean.

The park announced this week that 44 acres of harvestable shellfish area in the Seawall areas had been returned to open fishing because of the campground upgrade.

There are few clam flats in the reopened area because of the rock-bound coast, Mays said, but the newly re-opened Seawall flats should be productive.

Clams also can be harvested again in the Connor Point area of Southwest Harbor.

Much of the reopened area also should be fertile ground to drag for mussels, according to Mays and Fendl.

But Blue Hill shellfish dealer Rob Bauer is skeptical. He downplayed the reopening, saying the state could use its money in places that would have a far greater economic impact on the fishing industry.

For instance, he said, if the state remedied the discharges coming out of a sewer treatment plant in Machias, it would open up important clam flats that would have a significant economic benefit.

“It’s a lot of hoopla, and a lot of acres, but not a lot of economic impact,” he said.

He said real estate agents on MDI would likely benefit more from the discharge cleanups than the fishing industry.

Richard Green, a senior state environmental engineer, said Thursday that other discharges around MDI are being cleaned up.

For example, a closed area in the Salisbury Cove area of Bar Harbor is close to being reopened, said Green, who oversees the discharge cleanup effort for the Maine Department of Environmental Protection.

New projects, however, are now stalled because of lack of state financing, Green said. And because there won’t be a bond issue on next month’s ballot to raise more funds, he is not sure when it will be re-started in earnest.

If the Legislature does not fund the program next year in the new state budget, “eventually we’ll be at a point where we cannot proceed,” Green said.