The toxic algae that forms each summer on Lake Erie and other lakes around Ohio feed on phosphorus, a key element of livestock manure and sewage.

The first official forecast for 2017’s harmful algal bloom season is tentatively optimistic.

The amount of phosphorous in Lake Erie’s western basis is about the same as last year’s levels, barring unexpected extreme rainfall in the coming weeks, according to Tuesday's kickoff projection.

“If we go on as typical, we will be a little worse than last year,” said Rick Stumpf, a National Oceanic and Atmospheric Administration oceanographer who helps put together the weekly bloom projections.

“That’s the best-case scenario for this year: to match last year.”

The toxic algae that forms each summer on Lake Erie and other lakes around Ohio feed on phosphorus, a key element of livestock manure and sewage. Much of the phosphorus that gets into the lake comes from the Maumee River, which flows through eastern Indiana and western Ohio, depositing its waters into the western part of Lake Erie near Toledo.

Manure and sewage wash from soil and into the rivers and streams that feed the Maumee.

After low nutrient discharge levels in March and April, last week’s rainy weather spiked the amount of phosphorus flowing into the lake, according to the first weekly report released Tuesday by NOAA and Heidelberg University. Sometime this week, the current total phosphate load for the Maumee River is expected to surpass 2016 levels, which resulted in a moderate bloom.

"I wouldn't be terribly alarmed just yet, just because we had this rain event," said Laura Johnson, director of the National Center for Water Quality Research at Heidelberg University. “Just one small period of rainy weather doesn't guarantee a bloom.”

The severity of toxic algae hinges on unpredictable weather events, Stumpf said — and this spring has been particularly inconsistent.

“It’s hard to predict just how much rain we’re going to get," he said. "There’s a lot that’s uncertain right now.”

This year's unusually warm and dry winter might even aid in curbing harmful algae, as drier soils soak up rainfall and help prevent runoff, Johnson said.

As spring gives way to summer and scientists accumulate data, forecasts will become increasingly accurate.

“As we update this, our uncertainties will get smaller and we’ll replace forecasts with data," Stumpf said.

The weekly projections will continue through the end of June and culminate in a comprehensive seasonal forecast in mid-July.

In 2015, a monster toxic algae bloom blanketed Lake Erie after heavy June rains blew forecasts out of the water, said Johnson.

"So things in the next two and a half months could be fine — or things could get crazy," said Johnson, who also works to put together the weekly bloom reports. "The tricky part is using current levels to look in the future.”

In February 2016, the United States and Canada adopted phosphorus reduction targets as part of a 2012 agreement between the two countries to identify, address and prevent environmental issues in the Great Lakes region. The plan is to reduce phosphorus entering Lake Erie by 40 percent in the next 10 years.

In 2015, NOAA's forecast renewed calls that Ohio pursue a federal impairment designation for Lake Erie.

The designation is credited with helping the Chesapeake Bay fight its own algae problems by reducing the amount of algae-feeding nutrients that flow into the bay. The designation would almost certainly mean tougher regulations over how much manure farmers put down to fertilize their fields and over how large livestock farms deal with manure.

The designation brought about $2.2 billion for improvements to the Chesapeake Bay and could free additional federal money to help Lake Erie combat algae.

But Gov. John Kasich has refused to seek the designation, and Ohio Environmental Protection Agency Director Craig Butler has said the designation could slow existing efforts to reduce toxic algae.

Last month, a coalition of groups sued the U.S. EPA over the lake's impairment status.

mrenault@dispatch.com

@MarionRenault