People are being asked to boil their water before drinking it in all of Washington, DC and Arlington County in Virginia due to an increase in algae blooms in the Potomac River, as the nation’s capital prepares for its annual Fourth of July celebrations.

A boil water advisory was issued Wednesday night for the entire District of Columbia and neighboring Arlington County due to a spike in algae blooms in the Potomac River, officials said. The District of Columbia Water and Sewer Authority said the advisory,

Interstate Commission on the Potomac River Basin executive director Michael Nardolilli says a recent boil water advisory demonstrates a major vulnerability in the D.C. area’s drinking water supply.