Scientists from the National Oceanic and Atmospheric Administration warn that algae in Lake Erie are blooming. It’s not clear whether algal blooms are producing microcystin, the toxin that poisoned Toledo’s drinking water for three days last year. But the news highlights the need for continued urgent action against this menace.

It’s encouraging that leaders of Ohio, Michigan, and the Canadian province of Ontario are promising to cut by 40 percent over the next decade the lake’s levels of phosphorus, a substance that causes algae to grow. The administration of Gov. John Kasich deserves credit for taking the lead on this effort.

Though Indiana officials walked away from the talks, the regional agreement holds out hope for a healthier lake and a safer water supply. Lawmakers in Ohio and Michigan must continue to strengthen laws against phosphorus pollution to honor these commitments.

In the past 15 years, the amount of phosphorus dumped into Lake Erie has risen to record highs, and predictable consequences have followed, such as Toledo’s water crisis that affected nearly 500,000 people. Wastewater treatment facilities that discharge sewage into the lake contribute to the problem.

But two-thirds of the phosphorus deposited in the western basin of Lake Erie has come from fertilizer and manure runoff on farms near the lake’s tributaries, especially the Maumee River. A new law passed in response to the Toledo crisis prohibits Ohio farmers in the western basin from spreading fertilizer on frozen, snow-covered, or waterlogged soil, and from doing so on all land when forecasts predict heavy rain.

The law mandates certification and training for individuals who buy and apply manure from industrial-scale concentrated animal feeding operations (CAFOs). Wastewater treatment facilities along Lake Erie now must keep closer track of and report phosphorus levels.

In Michigan, similar regulations on fertilizer and manure are in force for residential and commercial lawns, as well as for CAFOs. But on Michigan’s farms, restrictions on the use of manure and fertilizer remain voluntary.

The new international agreement pact leaves up to each state and Ontario how to achieve phosphorus reduction targets. In Ohio, loopholes that might allow farmers to skirt penalties for improper application of fertilizer and manure should be narrowed. Greater state oversight of CAFOs also merits consideration.

In Michigan, fertilizer and manure regulations need to be toughened. In both states, more resources should be directed to water quality-control monitoring, which permits researchers to assess the success of agricultural regulations and practices in lowering phosphorus levels. According to a recent study by the Northeast-Midwest Institute, a research and advocacy group focused on the Great Lakes region, funding for such efforts remains insufficient.

Lake Erie is a vital resource for Ohio and Michigan. Vigilance remains essential to stop the next drinking-water crisis or swimming bans.

First Published July 1, 2015, 4:00 a.m.