A new U.S. Geological Survey (USGS) has found that pollution in New Jersey waterways has either declined or stayed the same over 40 years, but salt levels have increased.

Twenty-eight New Jersey streams were monitored from the 1970s through 2011. Researchers found that levels of nitrogen and phosphorous, which fuel algae blooms, decreased or remained the same.

Salt levels, however, increased over the years because the salt used to clear roads has been washed into the waterways.

These results are consistent with those found by a USGS study of streams in the Northeastern U.S. for a similar period of time, according to the report.

“Modernization of wastewater treatment plants, better stormwater management at the local level, decades of good work by the DEP and tough laws protecting rivers, streams and ecologically sensitive areas along them are resulting in healthier waterways,” said New Jersey DEP Commissioner Bob Martin.