Parts of Lake Michigan’s Green Bay have areas of low oxygen, which threaten aquatic life.
An Associated Press report says the “dead zones” are caused by high levels of nutrients, such as phosphorous. Runoff containing the nutrients flows into the lake, from farms, factories and wastewater treatment systems.
The report says the nutrients feed algae. When the algae die and decompose, the process sucks up large quantities of oxygen.
Tracy Valenta of the metropolitan sewerage district in Green Bay says the decline in oxygen could be the reason that the burrowing mayfly has disappeared from the area. The report says when the species is present, it indicates the ecosystem is healthy.