Residents of Toledo, Ohio’s fourth-largest city, spent the weekend under a water advisory after tests revealed toxins in the city’s water supply, likely caused by algae growing in Lake Erie.

Tens of thousands of people kept faucets turned off and left their homes in search of clean water. They waited in lines at fire stations for bottled water, crossed state lines in search of stores with supplies after local outlets ran dry, and drove to friends’ homes miles away to fill containers.

Early on Saturday, municipal officials asked the 500,000 residents served by the city’s water system to stop using tap water after the toxins were found at a city water treatment plant. The orders were clear: Do not drink the water, do not brush your teeth or prepare food with it, and do not give it to your pets. Health officials also advised that children and people with weak immune systems refrain from using the water to bathe.

With no indication of when the ban might be lifted, residents were preparing for days without clean running water. The Ohio National Guard brought 33,000 gallons of drinking water to the region, while volunteers handed out bottled water at distribution centers set up at local high schools.