Activities such as shellfish harvesting and swimming depend on safe water quality, which is tracked by measuring concentrations of bacterial indicators of fecal contamination. These water quality indicators are affected by point and non-point pollution, human (sewage) and non-human (animal) sources of pollution, environmental conditions, and climate change. Tracking these indicator organisms allows for evaluation of water quality relative to potential risks for human illness.

No increasing trends for fecal coliform bacteria, enterococci, or Escherichia coli bacteria.

Long-term data for tracking baseline (dry weather) trends in fecal indicator bacteria are only available for two currently monitored sites, Adams Point and the Lamprey River (Figure 15.1). At both sites, the long-term trends for enterococci, fecal coliforms, and E. coli have decreased since the last report, issued in 2018. This can be attributed, in part, to improved stormwater infrastructure and wastewater treatment at all facilities in the watershed. There was a significantly decreasing trend in the annual average concentration data (1988 – 2021) of fecal coliforms at Adams Point (Figure 15.2). Enterococci concentrations in the Lamprey River have significantly decreased from 1990 – 2021 (Figure 15.3).

The monitoring protocol is set up to assess baseline conditions and so it avoids wet weather, known to cause elevated contamination levels in the Great Bay Estuary.⁴⁴ However, since our region is forecast to receive more extreme precipitation events, these data do not reflect typical conditions, but rather, dry conditions.

State standard concentrations are included for each graph in Figures 15.2 and 15.3 as a reference, though the analysis procedures used for these data are slightly different than those required for assessing water quality classifications. Recent (2016 – 2021) levels of fecal coliforms at Adams Point (less than 5 colony forming units/100 mL) and enterococci levels in the Lamprey River (less than or equal to 24 colony forming units/100 mL) have, on average, remained below these reference concentrations, indicating acceptable quality. Generally, fecal indicator bacteria are present at elevated levels in estuarine tributaries that include urban centers at the head-of-tide, where there are more non-point sources, making the origin of pollution difficult to pinpoint. Head-of-tide urban centers may also have wastewater treatment facility discharges and significant impervious surfaces that cause runoff and increased stormwater-related contamination.

Excessive fecal indicator bacteria levels can be managed in various ways, informed by additional laboratory tests — microbial source tracking — that can identify the sources of the contaminating bacteria (e.g., humans, dogs, wildlife). This tracking tool can help managers identify a specific source so that the problem can be effectively addressed (e.g., replacement of a failed septic tank, education to manage pet waste). An ongoing study in the Lamprey River is using this tool to inform how best to ensure that river water quality is safe for recreational uses.⁴⁵

Other bacteria of public health concern include Vibro and some other naturally occurring bacterial species that are not a result of fecal pollution. The dramatic increasing trend in illnesses over the past 15 years, including gastroenteritis and wound infections, caused by Vibro species in the Northeast⁴⁶ is a regionally significant concern as coastal waters continue to warm.⁴⁷ Vibrio parahaemolyticus populations are increasing in the Northeast and in the Great Bay Estuary;⁴⁸ however, there have been only rare illnesses to date from exposure to New Hampshire coastal waters and shellfish.

Acknowledgments and Credit

Stephen Jones (NH Sea Grant/UNH).

Bacteria – Extended Report
Includes methods, data, and additional discussion not included in the Printed Edition.