The final Massachusetts Estuaries Project report on the health of Lagoon Pond was unveiled this week in Oak Bluffs, and the blunt diagnosis was summed up in two words: “significantly impaired.”

Dr. Brian Howes, technical director for the project, a joint venture of the state Department of Environmental Protection and the University of Massachusetts at Dartmouth, said that almost all of the 89 estuaries in southeastern Massachusetts are impaired. Lagoon Pond is no exception.

“People like to live near the coast and we discharge nutrients into coastal waters mainly through wastewater,” he said at a Wednesday night presentation at the town library. “It’s a big problem.”

In short, the last two decades have seen Lagoon Pond lose half its eelgrass beds, an economically and biologically vital ecosystem that plays a central role in the life cycle of juvenile scallops and fish. The culprit is nitrogen, an element vital to life on earth but in excess amounts disruptive to sensitive marine habitats, where it serves as plant food, fueling explosive algae growth that can muddy waters and rob sensitive photosynthesizing eelgrass of light. When the algae dies and decays, the water is then robbed of oxygen and the casualties can be more widespread than plant life.

“On the south shore of Cape Cod now every late July we typically see fish kills in a variety of ponds that were never there when I first moved there,” said Mr. Howes. Some estuaries on Cape Cod have not seen eelgrass beds since the 1960s, but Mr. Howes reassured the audience that the Lagoon still had time.

“Popponessett Bay went over the cliff 50 years ago,” he said of the Mashpee embayment. “You guys have your toes over the edge.”

Nitrogen comes from a variety of sources, from lawn fertilizer and agriculture to rainwater and atmospheric deposition. But by far, at least in Lagoon Pond, the largest source is from septic systems, according to the report. In fact, septic systems account for a full 79 per cent of nitrogen that town planners can control for (i.e. not from the rain or the air). Septic systems disinfect and treat wastewater before leaching it into the ground but do not remove nitrogen. After decades of development along its shores, the Lagoon was over its threshold, he said. As proof he cited a survey of Lagoon fauna that registered almost 800 animals at the well-flushed mouth of the Lagoon and only four at the most degraded and poorly-flushed area farther south at the Lagoon’s head, where oxygen depletion and murky water have stifled life.

“These are terrible conditions for animals,” he said bluntly.

Unlike some Cape towns that face decades of careful management to restore anything like a productive ecosystem, Mr. Howes said that Oak Bluffs could turn the tide against nitrogen pollution relatively quickly.

“It would take about ten years,” he said. “There could be four or five totally different fixes that cumulatively help restore the Lagoon and only one of them is wastewater.”

Six culverts along Beach Road could partially alleviate the situation, as could fertilizer education and increasing the residence time of water in the freshwater pond at the head of the Lagoon. But eventually, he said, sewers would have to be built.

“It might be possible that some combination of [these strategies] might actually be sufficient to bring the system to restoration, so there’s a lot of hope in here,” he said. “But it’s very likely you will not be able to restore this system without doing some wastewater infrastructure.”

Oak Bluffs is in the planning stage of sewering hundreds of houses along Barnes Road, and talks between the Oak Bluffs and Tisbury wastewater department are in the works.

One possible alternative on the minds of many in attendance was the use of composting toilets rather than multi-million dollar municipal sewer projects, after representatives from the Citizens for Economic and Ecological Sustainability of Falmouth gave a talk last week in West Tisbury extolling their virtues.

“Composting toilets would work only if you got rid of that compost by shooting it to the moon,” said Mr. Howes. Composting toilets sequester nitrogen but Mr. Howes suggested that it would be difficult to ensure that it didn’t end up back in the ponds.

Commercial fisherman Bill Alwardt spoke passionately about the effect the mismanagement of the pond over the past few decades had had on his livelihood.

“Being a fisherman, and I’ve fished that pond all my life, to me the sooner we start a project the better because I’ve seen this pond go downhill,” said Mr. Alwardt. “Even in the past year I’ve seen a die-off of eelgrass right at the mouth. I mean right on the flat just to the east of the opening. We’ve lost most of the eelgrass from the hatchery to Lagoon Road, if not all of it. I’ve seen a major die-off on that flat. It was there last year and it wasn’t there this year.”

“I believe it,” said Mr. Howes.