ST. PAUL — Officials with the Minnesota Pollution Control Agency are working to identify the effects of failing septic systems across the state.

Minnesota Public Radio News reports that there are about 500,000 homes in Minnesota from which wastewater flows into buried septic tanks — systems that are maintained, and often ignored, by homeowners. The agency estimates that more than 100,000 of those septic systems are too old or so close to the water table that they’re putting groundwater at risk.

Researchers have been testing hundreds of lakes and rivers across north-central Minnesota for contaminants and water quality.

None of the lakes examined in the most recent round of testing had clear signs of septic contamination. But researchers believe leaking sewage is almost certainly degrading the state’s waters.