TRAVERSE CITY, Mich. – The United States and Canada should crack down on sources of phosphorus runoff blamed for a rash of harmful algae blooms on Lake Erie, an advisory agency said Thursday. The algae produce harmful toxins and contribute to oxygen-deprived “dead zones” where fish cannot survive.

The International Joint Commission said in a report that urgent steps are needed to curb runaway algae – a problem that led both nations to reach their first agreement to improve Great Lakes water quality more than 40 years ago, when some considered Erie ecologically dead.

Tougher standards for municipal and industrial waste treatment produced improvements by reducing the flow into the lake of phosphorus on which algae feeds. But the problem began worsening in the late 1990s. In 2011, the largest mass on record formed in the lake’s western basin.

The report says different sources of phosphorus runoff have emerged – primarily large farms, where manure and other fertilizers are washed into tributary rivers during storms and snowmelt.

The report sets targets for sharp reductions in phosphorus runoff over three to six years, including a 46 percent decrease in total phosphorus and a 78 percent cut in the dissolved type for the lake’s central and western basins.

To reach those goals, governments in both countries should reduce the amount of phosphorus applied to fields and slow the flow of water to drainage systems, the report says. One step should be to ban spreading manure on frozen or snow-covered ground, it says.

Another proposal would link the cost and availability of government-subsidized crop insurance to farmers’ willingness to curb phosphorus runoff.

“Lake Erie was in a worse situation in the ‘60s and ‘70s ... and both nations took action and the lake came back. We’ve done it before and it’s doable now,” said Raj Bejankiwar, a commission scientist who led development of the report.