PITTSBURGH (AP) — Researchers at Carnegie Mellon University say a water quality problem in the Monongahela River that may have been linked to Marcellus Shale natural gas drilling is going away.

Jeanne VanBriesen said Thursday that preliminary data from tests this year showed that levels of salty bromides in the river have declined significantly when compared to 2010 and 2011. In many cases the bromides were at undetectable levels this year, and in general they returned to normal levels.