UPDATE: (CNN) -- A tap water ban affecting hundreds of thousands of people in Ohio was lifted after tests in affected neighborhoods returned "non-detectable" levels of an algae-related toxin Monday, Toledo Mayor D. Michael Collins said.
(CNN) -- Residents of Ohio's fourth-largest city will have to wait a little longer to use their tap water.
Tests conducted by both the state and federal Environmental Protection Agency showed high toxin levels in two neighborhoods in Toledo, Mayor D. Michael Collins said early Monday.
Instead of isolating the two neighborhoods, Collins said he'll keep the ban on drinking or using tap water in the entire city of Toledo until additional retests are completed. He declined to provide specifics on the names of neighborhoods in question and how high the toxin levels are.
"A majority of areas are satisfactory, but we have two areas of concern," he said at a news conference.
As many as 400,000 people were told not to consume, cook with or boil the tap water after a toxin called microcystin was found in the water supply Friday. Collins told reporters the advisories will remain in effect until further notice
Toledo's drinking water comes from Lake Erie, where a harmful algae bloom that causes microcystin has been growing.
The city has set up distribution centers for potable water, where members of the Ohio National Guard, fire officials and other first responders are giving out safe water.
About 350 Ohio National Guardsmen have been activated by the governor, according to a U.S. Defense Department official, adding that they have set up three Reverse Osmosis Water Purification Unit sites at two high schools and a police facility. The guardsmen have also delivered ready-to-eat meals, the official said.
Lining up for water
About two-thirds of the Toledo area population is affected by the water warning. Ohio Gov. John Kasich issued a state of emergency for Fulton, Lucas and Wood counties. The potential contamination also affects four municipalities in Michigan, CNN affiliate WXYZ reported.
There are no reports of anyone getting sick from the water, officials said.
When certain conditions are present, such as high nutrient or light levels, algae can reproduce rapidly, forming a dense population known as a "bloom," according to the National Oceanic and Atmospheric Administration
Testing is crucial because NOAA says it can't determine just from images whether blooms are toxic.
Ingestion of the toxin can affect the liver and cause nausea, diarrhea, vomiting and acute liver failure, according to NOAA. But the Ohio state emergency management agency said it is safe for adults to shower and for everyone to wash their hands.
CNN's David Shortell, Ryan Sloane, Barbara Starr, Marisa Marcellino, Donovan Long and Kristina Sgueglia contributed to this report.
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