AN IMPAIRED LAKE
In 2014, the Wisconsin DNR listed Green Lake as an impaired water body for a dead zone of low dissolved oxygen in its thermocline (a layer about 30-60 feet below the water's surface), likely caused by phosphorus.
For the GLA, this was a real call to action. We recognized that our organization had to step up in a substantial way to preserve this treasured resource. In response to these trends, we distilled our mission to one purpose: To be singularly focused on improving Green Lake's water quality.
With its impaired status and continued rain events that deposit more phosphorus in the Lake, the demands of repairing Big Green continue to grow. We're grateful to our strong partnership with the Wisconsin DNR to support our critical work.
WHY IS GREEN LAKE "IMPAIRED" & WHAT DOES THAT MEAN?
Impairment is a formal acknowledgment that a waterbody does not meet optimal water quality standards, as specified by the Environmental Protection Agency's Clean Water Act.
Water bodies that are listed as impaired are required to have restoration strategies to improve water quality. Entities implementing those lake restoration strategies have an increased likelihood of receiving grant funds.
In Wisconsin, nearly 1,700 lakes are impaired: 144 lakes for low dissolved oxygen and 718 lakes for high phosphorus. (All remaining lakes not listed as impaired are not necessarily meeting optimal water quality goals, but rather may not have had enough resources directed towards studying them to a level to determine that they are impaired.)
This impairment list is updated every-other-year by the Wisconsin DNR, and the trends are showing that we are still figuring out how to properly manage Wisconsin's natural resources.
LOW DISSOLVED OXYGEN
WHAT IS LOW DISSOLVED OXYGEN?
Dissolved oxygen is the amount of oxygen present in water. Fish and other aquatic organisms rely on dissolved oxygen to breathe. Lower levels of oxygen in the lake layer negatively impact the health of aquatic organisms.
WANT TO LEARN MORE?
We're conducting an ongoing study about Green Lake's phosphorus.
A Changing Lake: Addressing Low Dissolved Oxygen & High Phosphorus in Wisconsin's Deepest Natural Inland Lake, USGS/Michigan Technological University
Stephanie Prellwitz, Executive Director, Green Lake Association
Dale Robertson, Research Hydrologist, U.S. Geological Survey Wisconsin Water Science Center
Cory McDonald, Assistant Professor of Environmental Engineering, Michigan Technological University