With the help of citizen lake monitors, UW-Madison and the DNR have released a study of over 5,000 Wisconsin lakes showing nearly a quarter of them have become murkier in the past two decades.
It also shows this trend could get worse as a changing climate leads to increased precipitation. UW-Madison's Dr. Monica Turner was one of the lead researchers on the study. She says the use of satellite technology along with local monitoring data over many years provided data to conclude what is happening to lake water quality...
"....we had found that the clarity of the water had declined in about 23 percent of (the lakes). The clarity had improved in about six percent of them and the rest didn't change at all. We also found that water clarity was worse in a year that was wet and better in a year that was dry...."
She says runoff is key to understanding the change in clarity..
"...lakes that are very clear, ones that you can see 3.5 meters down were the ones most responsive to the differences between a dry and wet years. In other words, if you had a clear lake and we get a tremendous amount of precipitation during the year, those lakes drop in their clarity by about a meter. That means you can see down about a meter less...."
Turner says that is explainable by more surface runoff. She says northern lakes tended to have more clarity than their southern Wisconsin counterparts. One explanation is increasing rainstorm totals producing more runoff. In southern Wisconsin where there is more agriculture, more nutrient rich runoff made it into the lakes. Northern lakes tended not to see as much of that type of runoff. It also shows most lakes have stayed the same, and some are even seeing an improvement in water clarity.
A link to the study is here.