Mercer County and Hopewell Township officials say cleanup is underway in the Stony Brook after an emergency bridge repair released clay and silt into the waterway, turning sections of the stream cloudy and gray this week.
The incident occurred at the county bridge on Pennington–Hopewell Road (County Route 654) over the Stony Brook, near the Hopewell Valley Golf Course, where a contractor had been performing emergency safety work on the bridge. According to county officials, the contractor used clay in an earthen dam as part of the process that later washed into the brook.
County staff learned of the problem Tuesday evening after reports of murky water downstream. “We also became aware that the New Jersey Department of Environmental Protection (NJDEP) had been contacted over the weekend regarding a potential sediment discharge,” the county said in a statement.
That night and into Wednesday morning, county engineers and environmental staff assessed the site and coordinated with the Mercer County Soil Conservation District, NJDEP, and local leaders.
The county has since accepted a Notice of Violation from NJDEP related to the contractor’s actions, allowing remedial work to proceed. The County said that they have been given permission to use pumps and sediment-filter bags to remove excess material from the affected area of the stream.
Engineers said no sediment plume extended beyond Hopewell Township and emphasized that the clay consisted of “natural, clean fill from a quarry – not cement or chemically treated material.” And that “The observed turbidity was due to the natural color of the clay used on-site, which poses no known chemical or environmental threat to wildlife or humans,” according to the County release.
The Watershed Institute raises alarm
The Watershed Institute was among the first to sound the alarm after Executive Director Jim Waltman posted a video on Facebook showing the Stony Brook running cloudy and gray past the bridge. Standing along the bank, Waltman called the situation “a slow-moving environmental disaster” caused by sediment released from the repair site.
“This is the result of a construction project at the bridge on Route 654 in Hopewell Township,” Waltman said, explaining that a pile of material from the bridge site had “slid into the stream.” He noted that DEP had been alerted Saturday night, adding, “It’s now Wednesday morning,” with the water still carrying visible silt downstream.
Waltman warned that the Stony Brook is designated a Category One (C1) stream, a classification that provides among the highest levels of protection under state law.
According to NJDEP, “C1 waters are protected from any measurable change to existing water quality because of their exceptional ecological, recreational, water-supply, or fisheries significance” (N.J.A.C. 7:9B-1.4). These stricter antidegradation rules mean activities that could degrade the stream’s water quality face heightened scrutiny compared with standard waters.
“Nothing can live in the stream [in this] situation,” Waltman said. “Sediment will drop out, it’ll smother the mussels, kill the invertebrates, the insects at the bottom of the stream, and any fish that tries to swim through this.”
He urged immediate action from local and state officials: “We need DEP, Mercer County, [and] Hopewell Township to demand that this is cleaned up … This can just keep going downstream all the way to Princeton into Lake Carnegie if something isn’t done.”
Township: Swift action and ongoing coordination
Hopewell Township officials said they were notified Wednesday and moved quickly to coordinate a response.
“The Township Committee has taken immediate action to address concerns about turbidity in the Stony Brook,” the Township said in a release, noting that remediation work was underway, and that the water’s discoloration was expected to clear.
“The Township Committee and staff are committed to ensuring the health and safety of our natural resources,” the statement added. Township officials said they remain in communication with county agencies, NJDEP, the Mercer County Soil Conservation District, and The Watershed Institute.
What comes next
Mercer County continues to oversee on-site cleanup in coordination with NJDEP and county engineers. Officials said they will monitor water clarity and stream conditions to ensure the sediment removal effort succeeds.
The Watershed Institute said it plans to keep tracking the situation and has invited residents who observe continuing turbidity or sediment plumes to report them through the WarnDEP hotline.
