Crackrock Pond Foxborough

Crackrock Pond is covered with vegetation due to high phosphorus levels.

Phosphorus concentrations at Crackrock Pond failed to meet Environmental Protection Agency guidelines for the fifth year in a row, according to a report from the Neponset River Watershed Association.

The report says concentrations of phosphorus remained 10 times higher than the EPA standard throughout monthly sampling in 2021, which ran from May through October.

While the Neponset Reservoir upstream has struggled with phosphorus pollution for decades, the association first detected severely elevated concentrations of phosphorus at Crackrock Pond in 2017.

The concentration of phosphorus skyrocketed in 2019, when levels were 100 times higher than recommended. Though phosphorus concentrations have come down in the last two years, they are still well above the criteria for a healthy pond. As a result, the pond is covered in aquatic plants and the water is almost entirely devoid of oxygen.

“Phosphorus is necessary for plant growth, but naturally is found in very low concentrations. Because of this, it is often the ‘limiting’ resource in the freshwater environment. We tend to see algal growth when phosphorus concentrations increase — because all the other required nutrients are likely already there,” explains Sean McCanty, the association’s river restoration director.

“Aside from the aesthetic factor, the real problem is that when these extra plants and algae eventually die, they get eaten by bacteria. This process consumes oxygen — in extreme circumstances the dissolved oxygen levels get so low that fish and other animals die”, he adds. Data from the association’s water monitoring program show that low oxygen conditions, referred to as “hypoxic” conditions, were observed from June through September of 2021 below Crackrock Pond.

Other parameters that the association tests for, including pH and E. coli, were at acceptable levels, according to the state Department of Environmental Protection standards.

The water quality monitoring program that collects this data is part of a larger watershed restoration efforts. To view the report, visit