As summer fast approaches, the question topmost on the minds of most Bostonians is whether beaches will be open for swimming. Unlike Florida, the fear is not from sharks but from something far deadlier: pollution.

Heavy rain usually spells trouble for Boston beaches and it’s not uncommon for authorities to restrict swimming due to high pollution levels. But the water is relatively clear on dry days and swimmers have a field day. So last summer when a string of dry days saw dangerous levels of pollution, scientists were puzzled. An editorial in the Boston Globe called for the Massachusetts Water Resources Authority (MWRA) to continue to support attempts by UMass Boston researchers to identify the sources of this pollution. That endorsement is a public recognition of Urban Harbors Institute (UHI), members of the Environmental, Coastal, and Ocean Studies (ECOS) department, and others involved in UMass Boston’s 17-year commitment to cleaning up Boston Harbor. Back in the 1980s, when reports of massive pollution earned Boston Harbor worldwide notoriety, ECOS faculty began to study the harbor, and throughout that decade, served on many scientific advisory boards and carried out environmental research. Their aim was to lay the foundation for harbor cleanup by assessing the conditions, framing the issues, laying out options, and overseeing progress from a scientific point of view.

In 1989, efforts increased with the creation of UHI, which was founded to promote the environmentally sound and economically sustainable management of marine resources worldwide. The UHI basically conducts multidisciplinary research on urban harbor issues ranging from water quality and coastal resource protection, to harbor management, port planning, and integrated coastal zone management. Recommendations from the studies conducted are submitted to the government and also made public to several non-governmental organizations, like Save the Harbor/Save the Bay, for instance. This ensures constant public pressure on the government to act.

Last summer, water quality violations were most frequently recorded at Carson, Tenean, and Wollaston beaches. These unsafe levels were largely a result of storm water pollution after periods of heavy rain. Experts blame combined sewer overflow (CSO) for the problem. For anyone unfamiliar with the project, a “combined sewer” – owned by the Boston Water and Sewer Commission – is an older system that is designed to transport both street drainage and sewage. It is designed to overflow to the nearest water body during heavy rain so as to avoid flooding of streets and buildings. Currently, there are seven existing overflow points along the South Boston beaches and four along the reserve channel. Boston’s sewage system comprises 5000 miles of pipes connecting 42 townships and normally the Deer Island Treatment Plant treats all that waste, sending it through the sewage tunnel to be diluted in ocean currents. But during a heavy downpour, the plant is overwhelmed. So some pipes are redirected into nearby rivers, the harbor, and the bay, washing dog, bird, and even human waste into places where people swim.

The “rain leads to pollution” theory sounds quite convincing but it just doesn’t explain the pollution on dry days. “The CSO explanation is good to start with but we want to know what is causing the pollution on dry days. Suspects include boats dumping untreated sewerage, broken sewage pipes and illegal sewer outlets but we haven’t been able to actually pin down the real source,” says UHI director Rich Delaney.

That answer could come from ECOS scientist Bob Chen and fellow researchers, who have developed a laser-based detection system and a submersible data-gathering device to discover the sources of dryday pollution. Also engaged with the problems of harbor cleanup, biology professor Michael Shiaris has focused his work on the harbor since 1981. He is currently developing a technique based on DNA-fingerprinting to distinguish among strains of E. Coli in coastal waters and determine sources from among many potential polluters.

As this story goes to the press, the UHI has convened a Science Advisory Committee (March 11) that will bring together scientists from UHI, UMass Boston and other parts of the country to discuss pollution in the harbor and hopefully explain the source of dry day blues. Their detective work will decide whether Bostonians this summer cool off in the blue or watch it from a distance.