A recent federal survey found traces of a common, potentially harmful pesticide in nearly one-third of the nation's lakes.
The latest National Lakes Assessment, released by the Environmental Protection Agency this week, indicated that 30 percent of lakes contained low concentrations of atrazine, an herbicide linked to reproductive problems in frogs and serious health issues in humans.
Concentrations of the chemical, however, reached the agency's level of concern for plants in freshwaters in less than 1 percent of cases.
Agency officials were more concerned about high levels of nutrients such as nitrogen and phosphorous, which can cause algal blooms and stifle oxygen — and aquatic life — in the water.
Forty percent of lakes in the survey contained excessive phosphorus levels, while 35 percent saw high nitrogen levels. The study also showed that 31 percent of lakes had degraded communities of benthic macroinvertebrates, which include snails, mayflies and other small creatures.
"Nutrient pollution is one of America’s most widespread and costly environmental and public health challenges," the agency said in a statement. "EPA is working on many fronts to reduce the severity, extent, and impacts of nutrient pollution in our nation’s lakes and other waters."
The algal toxin microcystin was present in nearly 40 percent of lakes, but almost entirely in amounts below levels of concern set by the World Health Organization.
The assessment, which analyzed data from 2012, showed little change compared to the findings from a previous study in 2007. Levels of phosphorous, microcystin and potentially toxic cyanobacteria cells grew worse, but the EPA also said that lake water levels improved.
“We use lakes for drinking water, energy, food and recreation, and our fish, birds and wildlife depend on lakes for habitat,” said Joel Beauvais, the agency's deputy assistant administrator for water. “The National Lakes Assessment provides us with valuable information to help protect and restore our lakes across the country.”