University of Minnesota researchers studied 39 lakes, three major rivers and their tributaries and numerous wells around the Twin Cities and found about 70 percent of the road salt being applied in the metro area is being retained in the watershed. Heinz Stefan led the study, which found salt concentrations in the water has increased along with the usage rate. 

While current salt levels aren't harmful, Stefan says increases in sodium and chloride have been shown to decrease biodiversity in wetlands and reduce fish populations. He says more efficient use of road salt could help lessen the impact on the environment and save money.