Nassau County officials say a strain of E. coli has been detected in the water supply in the city of Long Beach.

Routine testing found the bacteria in water collected at a private residence. A robocall alerted residents to the discovery.

A boil water alert is in effect, meaning city residents should boil their water for at least one minute before using, or stick with bottled water.

The boil water alert only impacts the water system for the city of Long Beach.

A supply of water bottles donated by the county quickly ran out.

The boil water alert will remain in effect until every sample of water is clean of harmful bacteria, but the water is unsafe to drink until then.

"I repeat, the only water that should be consumed in the city of Long Beach is boiled or bottled water, even if you're brushing your teeth," County Executive Laura Curran said at a news conference. "Baths are OK, but if you're washing your hands before cooking, we recommend boiled or bottled water."

Curran says Long Beach immediately raised the chlorine level and was in the process of flushing out the entire water system.

Nassau's Health Department posted notices for people heading to the city's bars and restaurants. Tens of thousands of people are expected this weekend for Long Island Pride festivities in the city.

David Kilmnick, CEO of the LGBT Network, says: "We have plenty of bottled water and will be getting additional water all weekend on the boardwalk from Office of Emergency Management. We are now getting our ice from outside of Long Beach for anything that we would have to use it for."

There have been no reports of people sickened by toxins produced by E. coli. Symptoms vary from person to person, but some strains of E. coli can cause severe illness and death.

It's not yet known how E. coli got into the water supply. Long Beach officials say it could take up to three days to clear.

The county has an emergency hotline that can be reached at 516-227-9570.