The Merrimack River will briefly run red Tuesday, as officials use dye to test the flow of storm water around a local factory.
The Department of Environmental Services says a contractor for plastics manufacturer Saint Gobain will deploy red dye into the river in Merrimack.
They say the dye will show how surface water and storm water interact in the river. The dye could be visible in the water for up to two hours.
Officials say they've done similar tests in the past at wastewater treatment plants on the Seacoast.
The state is now overseeing long-term response to chemical pollution around Saint Gobain, two years after the factory allegedly contaminated local wells with PFAS toxins in air emissions.
To date, the company's response has involved millions in water service upgrades for private well users near the factory.