On Aug. 2, the City of Toledo, Ohio issued a water use ban for roughly 500,000 residents after chemists detected toxic levels of microcystin in the public water supply. Microcystin is a toxin produced by harmful algal blooms caused by the overuse of nitrogen and phosphorous fertilizers. Large amounts of excess fertilizers run off into waterways during rainstorms. Exposure to microcystin can cause diarrhea, nausea, liver dysfunction, and nervous system damage. Beyond the public health risks, harmful algal blooms also negatively impact ecosystems and burden the economy.

Despite these risks, the U.S. Environmental Protection Agency (EPA) does not restrict fertilizer runoff into our nation’s waterways. Nor has EPA set limits on allowable levels of microcystin or similar toxins in public drinking water systems or required testing for these toxins. Thankfully, some states have taken action in EPA’s absence. Ohio, for instance, has adopted the World Health Organization’s (WHO) recommended maximum concentration of one microgram per liter, equal to roughly two Olympic-sized swimming pools of the toxin in Lake Erie.

As a result of state monitoring requirements and prompt action by local and state officials, public exposure to the toxin was minimized in Toledo. Though major health impacts were apparently avoided in this case, harmful algal blooms wreak havoc on ecosystems and impose enormous costs on nearby communities.

Public health emergencies that require large-scale water use bans for multiple days, such as the contamination in Charleston, West Virginia and now in Toledo, can also undermine public trust, especially when officials appear to be withholding critical information. For example, when Toledo’s mayor, D. Michael Collins, lifted the water ban early Monday morning, residents remained skeptical of the water’s safety and successfully called on Collins to publicize the latest test results. And even with the ban lifted, the city has asked residents to “continue conservation efforts during the algal season, which typically lasts until September.”

The impacts associated with uncontrolled fertilizer runoff are not unique to Toledo or Lake Erie. “What plagues Toledo and, experts say, potentially all 11 million lakeside residents, is an increasingly serious problem across the United States,” writes Michael Wines of The New York Times. In fact, EPA warns that harmful algal blooms are a “major environmental problem in all 50 states.”

Instead of waiting until another emergency strikes, we need to proactively prevent fertilizer runoff from contaminating water supplies, threatening ecosystems, and negatively impacting the economy. Strong preventative actions should include federal rules designed to reduce the amount of fertilizer entering our waterways and to limit the concentration of contaminants in our public water systems. States should also have the ability to set more stringent standards than the federal minimums. Together, these rules would not only drastically reduce health, environmental, and economic risks, but would also boost public confidence in the safety and quality of our drinking water and in public protection programs generally.

Editor's note: This post has been updated.