NEW BEDFORD, Mass. — Shellfish offer some of the best remedies for the environmental problems confronting the state’s coastal areas. For example, poor water quality — often the result of nitrogen loads from failing septic systems, discharges from sewage treatment plants and/or the overuse of fertilizers — threatens coastline health, and shellfish can play a big part of the solution.

As it feeds, an adult oyster can filter up to 50 gallons of seawater daily, according to Jon Kachmar, coastal director for The Nature Conservancy in Massachusetts. “Oysters are incredible filters,” he said during a late-March talk titled “Restoring Rivers and Estuaries, Native Fish and Shellfish” at the New Bedford Whaling Museum. “The ability of oysters to reduce nutrients is an important part of the picture, but we shouldn’t overemphasize it. But it certainly needs to be part of the discussion.”

Besides improving water quality by filtering impurities, oyster beds — and shellfish beds in general — provide important ecosystem and economic services, such as providing food and habitat for birds, finfish and other marine life, sustenance and recreation for people who harvest wild oysters, and coastline protection from waves and storm surge.

To help address coastal water-quality issues and better protect fragile coastal environments such as salt marshes and seagrass beds in Massachusetts, Kachmar is leading an ambitious initiative to restore native shellfish species, most notably oysters, and their habitat to some 5,000 acres.

The initiative began about two years ago with the collection of wild larval oysters, known as spat, in various coastal waters to determine natural recruitment. The effort’s goal is to restore 5,000 acres of native shellfish beds by 2050. Restoration projects are planned for the North Shore, South Shore, Boston, Buzzards Bay, and Cape Cod and the Islands, according to Kachmar.

Two years ago, The Nature Conservancy and its partners launched a small oyster restoration project in Tisbury Great Pond on Martha’s Vineyard. In Boston, the city, the state, Northeastern University and The Nature Conservancy have received funding to consider using dredged materials from a planned 2017-19 project to build new reefs in Boston Harbor. These 3-D structures would provide important habitat for shellfish, according to Kachmar.

About a century ago, wild reefs bustling with life were so large ships had to navigate around them. By the 1970s, however, intense harvesting, pollution and disease had destroyed many of them. Extensive wild oyster beds are now few and far between, and exist mostly in the Pacific Northwest and New Zealand, Kachmar said. In fact, 85 percent of oyster reefs globally have been lost in the past five decades.

In Wellfleet, which literally was built on shellfish, The Nature Conservancy, Mass Audubon, the National Oceanic and Atmospheric Administration (NOAA) and the town are experimenting with different structures on which oyster spat can stick, with the goal of rebuilding a reef that is expected to bolster local populations of shellfish and provide benefits such as clean water and defense against rising seas.

To survive, spat attach themselves to hard surfaces. Oyster beds begin to develop when free-floating oyster larvae attach themselves to such surfaces. Clam shells are often used to build new oyster beds. From that point, the spat can mature into adult oysters.

“Oysters and shellfish are very important ecologically,” Kachmar said. “They’re important for recreational and commercial fishing. They provide lots of benefits.”