April was the first month of the TRWA 2026 water quality monitoring season. The numeric results are on our Monitoring Results website page.
The results for nitrate downstream of the Brockton wastewater treatment plant (WWTP) were higher than the Mount Hope Bay water quality target of total nitrogen 0.45 mg/l however by the downstream Church St sampling station in Raynham the river met this criterion. The results for total phosphorus were all below the EPA Gold Book freshwater stream criterion of 0.100 mg/l with the highest values below the Brockton WWTP. The bacteria levels exceeded the EPA enterococci water quality criterion of 35 colony forming units (CFU) at five locations but by much smaller amounts than we often saw last summer. The highest was at Church St in Raynham a short distance below an area where townhouse construction is underway relatively close to the river bank.
It is noteworthy that at the beginning of April river flow was 1250 cubic feet per second (cfs) as measured at the USGS Bridgewater gauge. The day we sampled (4/14/26) river flow was 621 cfs. The beginning of May river flow was only 294 cfs. The mid range river flow when we sampled and the fact that it had been two weeks since significant rainfall which brings stormwater pollution and bacteria into the river all contributed to the relatively good water quality results measured in April. In May we are seeing the river return to a flow level comparable to what we saw in May 2025 when the river flow eventually declined into severe drought conditions of around 50 cfs from August through early October. It will be important to see if drought flows return to the watershed’s rivers and streams in 2026 and if we monitor the same adverse water quality impact of low flows coupled with stormwater pollution from intense short duration storm events. These summer storm events, a product of global warming, deliver pollution but do little to quench the thirst of the watershed’s rivers and groundwater table.
Because of the outsized adverse impact of stormwater pollution on our water quality TRWA supports the Watershed Protection Standard (WPS) in partnership with the Southeast New England Program (SNEP) Network, the watershed’s Regional Planning Agencies and our Environmental Organization partners. To address the twin challenges of development and climate change municipalities need support in adopting the latest science and techniques which allow new development to: maintain pre-development groundwater recharge volume, maintain pre-development nutrient (nitrogen and phosphorus) export loads from the site, and maintain a resilient landscape as determined by response to extreme storms and manage runoff to pre-development volume.