A third of Ohio’s farmland is loaded with too much phosphorus that comes from farm fertilizers and livestock manure and is known to feed algae that have become a growing problem in Lake Erie and Ohio’s inland lakes, researchers have found.

Ohio State University researchers tested a million soil samples from across the state and found that most of the samples tested over time showed the amount of phosphorus was actually being reduced, according to a report released Wednesday.

But that doesn’t mean the outlook for this year is better for Lake Erie, said Jeff Reutter, director of Ohio State’s Stone Laboratory near South Bass Island.

Heavy rains this spring have washed more phosphorous off fields and into streams and rivers that pour into the lake.

“It’s basically getting a little bit worse every year,” Reutter told the Ohio Lake Erie Commission during a meeting Wednesday.

Algae in Lake Erie used to be limited to its western basin between Toledo and Sandusky, but it’s now moving into waters closer to Cleveland, he said.

It’s also becoming a problem in Ohio’s smaller lakes. The state posted water warnings at several lakes last summer, going as far as warning against swimming, boating and fishing at Ohio’s largest inland lake, Grand Lake St. Marys, between Toledo and Dayton.

Warning signs already have been posted this year at Grand Lake and Buckeye Lake in central Ohio.

Ohio’s phosphorus levels are consistent county to county except around Grand Lake, where there are problems with animal manure runoff, Reutter said.

Reducing phosphorous levels won’t be easy, he said.

Farmers should begin by reducing how much fertilizer they use in the fall and eliminate use in winter when the ground is frozen, he said. “Phosphorus reduction is the best strategy,” he said. “We think you’ll see an almost immediate improvement.”

James Zehringer, director of the Ohio Department of Agriculture, said his department will be working more closely with farmers on how to better apply fertilizer to their fields.

The agricultural industry is relying on farmers to make changes on their own, but critics have said the voluntary programs aren’t enough.