The U.S. Environmental Protection Agency won't declare Ohio's western end of Lake Erie impaired by toxic algae, siding with state regulators who say they are making progress in tackling the problem.

The decision released Monday means Ohio will continue to take the lead on fighting the algae blooms that in recent years have fouled drinking water in the shallowest of the Great Lakes.

The EPA said it recognizes the state's ongoing efforts to reduce pollution feeding the algae.

Several environmental groups have been pushing the EPA to make the impaired watershed designation and pave the way for increased pollution regulations. Those groups last month sued the EPA to force the agency to make a decision on whether the western part of the lake should be declared impaired under the Clean Water Act.

"By any measure, western Lake Erie does not meet the Clean Water Act's standards of fishable, drinkable, and swimmable for significant portions of the year," said Molly Flanagan, of the Alliance for the Great Lakes.

She said the decision fails to protect drinking water and recreational opportunities for people along the lake.

In this Aug. 21, 2013 photo, a dredge barge works along the edge of a large algae bloom in the Toledo shipping channel in Toledo, Ohio. Toxins from the algae blooms on western Lake Erie are infiltrating water treatment plants along the shoreline, forcing cities to spend a lot more money to make sure their drinking water is safe. (D'Arcy Egan/Plain Dealer/Associated Press)

Michigan last year asked the EPA to designate its portion of Lake Erie as impaired. Ohio resisted making the same request and asked for only some shoreline areas to be put on the impairment list. The EPA agreed to Ohio's plan. The agency didn't immediately respond when asked about the request from Michigan Tuesday.

While steps have been taken in Ohio and Michigan to reduce the farm fertilizer runoff and municipal sewage overflows that feed the algae, environmental groups and some political leaders have become frustrated by the pace and depth of those efforts.

The sometimes toxic algae are a threat to both drinking water and wildlife and have become more prevalent in recent years.

Blooms in the western end of the lake blanket its waters and turn the lake into unsightly shades of green in most summers. An outbreak in 2014 contaminated the tap water for more than 400,000 people around Toledo.