Algae and Hydrilla are back in our reservoirs, and so are the chemicals used to treat them. Are they bad for the fish?

Recent scientific research suggests that copper sulfate and fluridone, common treatments for algae and Hydrilla, respectively, can have subtle harmful effects on fish.

Hydrilla

Between now and August, New York City’s Department of Environmental Protection (DEP) will be using chemical treatment in four local reservoirs to control overgrowth of algae: The New Croton, Muscoot, Cross River, and Croton Falls.

The DEP will also be treating the New Croton Reservoir for Hydrilla, an invasive weed that was first discovered in the reservoir, and in the Croton River, in 2014.

As many readers will know, these reservoirs are part of NYC’s vast reservoir system, which delivers more than a billion gallons of water each day to The Big Apple. According to city and state officials, the chemicals used—copper sulfate pentahydrate for algae and fluridone for Hydrilla—do not affect human health at the low concentrations that end up in the water supply.