ST. PAUL — Minnesota cities are seeing an increase in emergency sewage discharges as they struggle with rainfalls that can overwhelm systems that collect and treat wastewater.

Cities such as North Mankato are dealing with rising waters. The city has released more than 4 million gallons of untreated sewage into the stormwater system since a June flood.

Experts said these emergency discharges are happening more often, as cities grapple with a rise in extreme rainfalls.

The Minnesota Pollution Control Agency said that since 2010, wet weather has effected wastewater treatment operations an average of 143 times a year, which has resulted in raw or partially treated sewage overflowing or being discharged into the environment.

More than 140 cases have been reported so far this year.

“Without a question, we’re going to see these kinds of events happening more frequently in Minnesota,” said Trevor Russell, water program director for the advocacy group Friends of the Mississippi River.

He said a combination of the changing climate and aging water infrastructure will eventually cause sewer problems.

“Our concrete, our wastewater treatment systems, our pipes, our ponds were built 30 to 50 years ago with 30- to 50-year life spans,” Russell said. “And most of that stuff needs to get replaced far more quickly than we’re investing in their replacement.”

Aging pipes that are cracked can allow clean groundwater to flow into the sewer lines, which can cause problems when combined with the extra water that comes with record-breaking precipitation.