Freshwater lakes like Lake Monona, seen here in Madison, Wisconsin, are in danger as salt used to de-ice frozen roads makes its way into the nation's waterways.

(Premium UIG/Getty Images)

Freshwater lakes in the United States are becoming dangerously salty, scientists say, thanks to our use of salt to de-ice frozen roadways during the winter months.

According to , northern freshwater lakes are being increasingly salinized by the saltthat runs off impervious surfacesand leaches into the nation's waterways.

More troubling is the finding that within 50 years, many of these lakes may become uninhabitable for aquatic life if nothing is done to curb the amount of salt reaching freshwater lakes.

The scientists studied 371 large lakes in the North American Lakes Region from Minnesota into Maineand found that lakes located within 1,640 feet ofpaved roadswere more likely to have rising salinity.

Only lakes larger than 10 acres that had at least 10 years of data were reviewedfor the study. The researchers looked at how many roads were nearby and determined that even if only 1 percent of the land within the 1,640-ft. buffer zone had paved roads, the likelihood of increased salinity was almostguaranteed.

While salination levels of lakes can change dependent upon environmental factors like drought, “road salt is the major driver for chloride loading,” study co-author Hilary Dugan, aUniversity of Wisconsin-Madisonfreshwater expert,.

The chemicals used to de-iceroads, sidewalks and parking lots is similar to table salt, or sodium chloride. Its use became prevalent in the 1940s, according to the study.

Chloride trends for North American freshwater lakes.

(PNAS)

Chloride concentrations can rangefrom 0.18 to 240 milligrams per liter for all lakes, with a median of 6 milligrams per liter. In contrast, seawater .The recommended maximum level of chloride in U.S. drinking water is 250 milligrams per liter.

As salt use to de-ice roads continues to rise, more and more of the chloridefinds its way into streams, rivers and eventually lakes, where it accumulates over time.This, the scientists note in the study, can "alter the composition and function of phytoplankton, zooplankton, macroinvertebrate, and fish communities."

Of the lakes studied, 44 percent showed evidence of long-term salinization.

"Expanding on this finding, thousands of lakes in these regions are at risk of long-term salinization,"the scientists said. "Keeping lakes 'fresh'is critically important for protecting the ecosystem services freshwater lakes provide, such as drinking water, fisheries, recreation, irrigation, and aquatic habitat."