On Sunday, Toledo mayor D. Michael Collins called decreased levels of toxins in the city's water supply a positive sign. Officials had initially warned residents on Saturday not to drink tap water, after tests at a treatment plant showed readings for the microsystin toxin above the standard for consumption, possibly because of algae on Lake Erie.

"All I can tell you is that everything is trending in a very positive direction," Collins told reporters on Sunday. However, he cautioned that "this is not over yet" and he could not predict when residents might return to safely drinking water from taps that drew from Erie, the shallowest of the US's five Great Lakes.

Saturday's warning effectively cut off the water supply to Toledo, most of its suburbs and a few areas in southeastern Michigan. Stores have reported shelves emptied of bottled water. Many residents drove to other states in search of fresh water.

Ohio Governor John Kasich has declared a state of emergency, ordering the state's National Guard outfit to deliver purification systems, pallets of bottled water and ready-to-eat meals to residents in several counties. Officials instructed residents not to boil water because that increases the toxin's concentration.

Though Collins has received no reports of residents sickened from the water, he warned that children should not shower or bathe for the time being and that residents should not give it to pets.

'Harmful algal bloom'

Over the weekend, health officials sent samples to several laboratories for testing after finding that a "harmful algal bloom" may have begun to grow in Lake Erie, Ohio Environmental Protection Agency spokeswoman Heidi Griesmer said. Algal blooms during the summer have become more frequent and troublesome around the western end of Lake Erie.

Phosphorous in runoff from farm fertilizer and sewage treatment plants feeds the algal growth, leaving behind toxins that contribute to oxygen-deprived dead zones where fish cannot survive. The toxins can also kill nonaquatic animals and sicken humans, affecting the liver and causing diarrhea, vomiting, nausea, numbness or dizziness.

The effect can happen in any body of water with access to agricultural waste and hot summers. The World Health Organization has reported such blooms in Australia, Japan, Israel and Germany.

mkg/jr (Reuters, AP)