Cribbing a famous line from an infamous late U.S. president, it is public enemy number one in Southeastern Massachusetts, although this time the enemy is not drugs but nitrogen. Nitrogen poses a serious threat to the health of our coastal ponds and saltwater embayments that were once pristine and are now in alarming states of decline. Eelgrass beds are gone or disappearing, and along with them the clean shellfish that both provide a rich source of food and form a key cog in the local economy.

Here is our elementary lesson in marine biology: Too much nitrogen spurs the growth of algae which in turn blocks sunlight, inhibiting the growth of eelgrass and taking up oxygen in the water column. The extreme end of this cycle for a pond is anoxic conditions, which cause shellfish to die.

Thankfully, most Vineyard ponds have not yet reached that stage; the same cannot be said for the saltwater estuaries along the South Shore of the commonwealth. For the better part of the last decade the Massachusetts Estuaries Project has been actively engaged in research to pinpoint the sources of nitrogen entering the saltwater ponds in a region stretching from Duxbury to Cape Cod and the Islands. Septic system discharge, acid rain and waterfowl are among the culprits.

Sponsored by the University of Massachusetts at Dartmouth and the Massachusetts Department of Environmental Protection, the estuaries study combines intensive water sampling with sophisticated computer modeling techniques to develop detailed profiles of the health of the ponds.

The work has been slow at times, due to sporadic problems with funding and a few political bumps in the road. And so far the sampling has yielded more data than solutions. During a recent presentation to the Chilmark selectmen by study director Dr. Brian Howes, selectman Warren Doty, a longtime advocate for the inshore fishery, questioned the value of the study. “What is this going to tell us that we don’t already know?” he asked.

Mr. Doty’s frustration is understandable. Documenting the problem alone won’t make it go away. But the Massachusetts Estuaries Project is a valuable tool, and seems well worth its modest cost to establish a baseline of data that can be used to measure progress against the scourge of nitrogen in our ponds.

As for what to do with the information, that ultimately will be up to the individual towns; the leaders of the estuaries study have been quite clear about this from the start. Some Vineyard towns may decide to expand their sewer systems to protect the ponds, an expensive option that will demand careful scrutiny and thorough public debate when the time comes.