New national guidelines are being developed by the U.S. Environmental Protection Agency to protect swimmers and kayakers from the growing threats posed by toxic algae in lakes and rivers.
Agency officials said the focus will be on people who are likely to swallow water during recreational activities.
The EPA issued a report to Congress last week saying that it also will be looking at whether new health advisories are needed on algae toxins in drinking water.
Harmful algae blooms have been expanding rapidly in both numbers and intensity, the EPA said.
An algae bloom that spread across Lake Erie last summer was the largest on record, government scientists said earlier this month, while another toxic algae outbreak stretched more than 600 miles along the Ohio River through four states.
Tackling the problem has taken on greater urgency since toxins from algae contaminated the tap water for 400,000 people in northwestern Ohio and southeastern Michigan in August 2014.
The EPA said in its report last week that there are information gaps when it comes to understanding toxic algae.
One of the challenges is "an incomplete understanding of how to prevent, predict, analyze, monitor and treat toxins in drinking water," the report said.
Those toxins can cause rashes, diarrhea, vomiting and breathing difficulty. In some cases, it can lead to liver, kidney and nervous system problems. But not all algae blooms are toxic.
Scientists say climate change and higher levels of nutrients such as phosphorus seeping into waterways may be why they're seeing a rising number of algae contamination cases.
The EPA said it will work with states and water treatment plant operators to update guidelines on monitoring drinking water for algae-produced toxins while also looking at treatment plans.
It also plans to take steps toward improving the quality of the lakes and rivers that supply drinking water, including putting more funding toward limiting nutrient pollution that feeds the algae in the Great Lakes.
A draft of the proposed guidelines for swimmers is expected to be released by summer, the EPA said last week. It may also look at exposure limits for coming into contact with toxins in the water if there is enough data.
The guidelines will look at two specific toxins produced by blue-green algae.
Nineteen states already have their own regulations. They are California, Illinois, Indiana, Iowa, Kansas, Kentucky, Massachusetts, Nebraska, New Hampshire, North Carolina, Ohio, Oklahoma, Oregon, Rhode Island, Texas, Vermont, Virginia, Washington and Wisconsin.