The dye tablets, which D.C. Water said are nontoxic and biodegradable, cause creek water to become green. Moving water will then flush and disperse the dye.
The dye allows D.C. Water technicians to observe and record where the dye exits pipes.
The effort is part of D.C. Water’s Clean Rivers Project to reduce the volume of combined sewer overflows, which occur during periods of rainfall when a sewer’s capacity to hold water is exceeded. When this happens, sewer regulators let the excess water, a combination of stormwater and sanitary wastes, be discharged into the District’s rivers and creeks, according to D.C. Water’s website. Reducing these overflows improves water quality to Piney Branch, Rock Creek and the Potomac River.
Lisle said dye testing is common practice and done across the country, often to investigate leaks along sewer lines. He said D.C. received calls from residents during similar testing a few years ago after someone posted a photo of the green dye on social media.
This time, Lisle said, D.C. Water put out a release to give residents advance notice. It led to humorous reactions, which he said is good because that means people are spreading the word about the water.
“It isn’t even St Patrick’s Day @dcwater!” one user wrote on X.
Lisle said the dye testing is estimated to last one day, but it could take longer for the dye to dissipate, depending on the weather.
“Because the creek is so slow moving, it could take maybe two days for the dye to be completely gone,” Lisle said. “Our hope is that won’t be the case and that it will wash out quickly.”
D.C. Water said traffic on Piney Branch Park will not be impacted by the work.
Read More: Rock Creek Park water temporarily turns green due to drain dye testing