New York City’s sewers, whose lore has spawned films, children’s books and fantastical tales of alligator infestation, have now seized a role in the pandemic: Scientists are tracking outbreaks by monitoring the smelly, gray effluent that flows through underground pipes in hopes of identifying coronavirus clusters days before they appear through patient testing.

The undertaking, which has ramped up in recent weeks, has mirrored efforts across the country to surveil waterways for viral components, flushed down toilets by infected Americans who are excreting it in feces, even when asymptomatic or pre-symptomatic.

Rising traces of the virus were detected in New York in recent months in wastewater samples scooped from sewage treatment plants near coronavirus hot spots in Brooklyn, Queens and Staten Island. But now, scientists say, increases are being seen citywide, as infection rates reach their highest levels since the spring.