by Martha Morgan

Water quality in the Nashua River has improved dramatically over the past three decades. The river once was recognized as one of the ten most polluted rivers in the U.S., and was infamous for its daily color changes and odor. Today, many segments of the river are marvelous for canoeing, and some brave souls even swim occasionally with no ill effects. However, when the Nashua River Watershed Association receives calls from parents asking if the river in a particular segment is safe for swimming (usually after their children have already taken the plunge), we generally have to caution that we're not sure on a day-to-day basis if the bacteria levels support swimming, and we certainly don't recommend swimming after storm events.

Bacteria levels rise in the river following rain events, partially due to urban runoff, but also due to combined sewer overflows (CSOs) in the cities where sewer pipes and storm drains share the same drains. Rainwater from large storm events exceeds the sewers' capacity for handling the flow, with the result that rainwater and raw sewage are diverted directly to the river.

The City of Fitchburg has a Consent Order from the EPA to remedy the combined sewer situation, but is not required to have the work completed until 2020. The City of Nashua also is required to separate the storm drains. Indeed the remedies are very costly and are a huge burden for a city budget.

In 1998, the Massachusetts Department of Environmental Protection, Division of Watershed Management (DEP-DWM) conducted extensive sampling in the watershed as part of the Massachusetts Watershed Initiative's rotating 5-year Basin Cycle. The resulting report, titled "Nashua River Basin 1998 Water Quality Assessment Report", can be viewed at: www.magnet.state.ma.us/dep/brp/wm/wmpubs.htm. The report explains in detail the sections of the river which fall into the categories of "support", "partially support", non-support", or "not assessed" for the following uses: Aquatic Life, Fish Consumption, Primary and Secondary Contact Recreation, and Aesthetics. This report lists portions of the North Nashua and mainstem Nashua rivers and nine lakes in the Nashua River Basin on the 1998 list of impaired waters. Impairments are due to elevated bacteria levels, nutrient levels, sedimentation and/or toxicity.

Combined sewer overflows and municipal wastewater treatment plants are not solely to blame for elevated bacteria levels in the river. Homes have been densely settled adjacent to the river and tributaries in areas where today's regulations would have prohibited development. Wetland soils near rivers are not amenable to septic systems. Some municipalities are in the process of remedying this. For instance, Lancaster is placing sewer lines in some of the areas with homes adjacent to the river, which should help prevent failed septic systems from contributing to increased bacteria counts along that section of the river. It should be noted that sewers have adverse impact on streamflow through reducing infiltration and inflow (I/I) of adjacent surface and ground water, so where sewers might mitigate a water quality problem they might exacerbate a water quantity problem in some situations.

Agricultural activities, despite being diminished since burgeoning development has replaced fields with housing lots and asphalt roads, still contribute bacteria and nutrients to the watershed. Excess nutrients from fertilizers on agricultural fields and suburban lawns produce excessive amounts of plant growth in ponds and streams. The decaying of the plants consumes dissolved oxygen needed by aquatic life, and often results in offending odors. An overgrowth of noxious plants covers swimming areas in ponds and contributes to pond eutrophication. Pepperell Pond, a Nashua River impoundment, is a "sink" in the river for phosphorus, which results in green algae blooms that cover the pond in summer.

Two rivers in the basin are considered excellent cold water fisheries: the Squannacook and the Nissitissit Rivers. All but the lowest reaches of these two rivers support all of the potential uses listed in the DEP report. A major threat to these and other tributaries is suburban development, which in turn leads to increased sedimentation and nutrient runoff. Nutrient loading to the river from treatment plants may be addressed by updated, stricter controls in discharge permits. Development pressure along tributaries must be addressed through local controls, planning for growth and natural resource protection, and efforts to preserve open space. Water quality can best be maintained or improved through these joint efforts.