For many residents of the Casco Bay region, clamming represents an important tradition, as well as a livelihood. The economic value of this resource has been limited by the widespread threat of bacterial contamination. Malfunctioning or improperly maintained septic systems, nonpoint-source pollution, overboard discharge systems, boat discharges, and combined sewer overflows have closed many shellfish flats to harvesting.

The Casco Bay Estuary Partnership is working with state, local, and citizen partners to reopen closed clam flats. This effort promises both ecological and economic benefits: closed flats in Casco Bay could provide clam harvests worth $3.7 million/year in extra earnings.

Bacterial contamination from sewage also causes closures of swimming areas at Willard Beach, South Portland; Peaks Island; and East End Beach in Portland. The U.S. Environmental Protection Agency (EPA) initiated the Beaches Environmental Assessment, Closure and Health (BEACH) Act of 2000 in response to the growing concern about public health risks posed by polluted coastal bathing beaches. The Maine Healthy Beaches program is taking a leading role in this initiative.

Shellfish flats and swimming areas are closed when elevated bacteria levels indicate the presence of human or animal waste, since exposure to contaminated water and shellfish can cause illness. Too many nutrients, especially nitrogen, can pose additional problems for shellfish harvesting and the bay. Sources of bacteria and nitrogen include septic systems, overboard discharge systems, municipal and industrial discharges of wastewater, illegal sewage discharge from boats, and polluted stormwater runoff.