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Sanitary Sewer Overflows

What is a Sanitary Sewer Overflow?

A sanitary sewer overflow is a release of untreated or partially treated sewage from a sanitary sewer system. Sanitary sewer systems collect and transport sewage in and around Duluth via pipes and pumps to the Western Lake Superior Sanitary District (WLSSD) wastewater treatment plant. At the treatment plant, sewage is treated before being discharged into the St. Louis River.

What causes Sanitary Sewer Overflows?

Sanitary sewer overflows can occur for a variety of reasons including:

• Blockage. Sewer lines can become blocked by debris such as fats, oils, and grease (FOG), as well as wipes (including flushable wipes), tampons, and other non-flushable items. When a sewer line becomes blocked, sewage can back up and overflow from manholes and other openings in the system.
• Inflow and Infiltration. Sewer systems can also be impacted by inflow and infiltration (I&I). I&I refers to the entry of stormwater and groundwater into sanitary sewer lines. I&I can occur through cracks and defects in sewer lines, as well as through improperly connected downspouts and sump pumps. During heavy rainstorms, I&I can overload sewer systems and lead to overflows. For additional information, visit the Inflow and Infiltration fact sheet.
• Equipment Failure. Sewer overflows can also be caused by equipment failure, such as power outages or pump failures.

Impacts of Sewer Overflows

Sewer overflows can have a significant impact on public health and the environment. Untreated sewage contains harmful bacteria and viruses that increase the risk for diseases, including gastroenteritis, hepatitis A, and typhoid fever. Sewer overflows can also pollute waterways and damage aquatic ecosystems.

What to do if you see a Sewer Overflow?

Report any water overflowing from a manhole to WLSSD as soon as possible and avoid contact with any sewer overflow due to the potential for exposure to disease-causing organisms.  Water from sewers may also lift and move manhole covers creating dangerous fall hazards when the overflow ceases.  WLSSD staff can be contacted at 218-722-3336 24-hours per day to report overflowing manholes or any open manhole.

How to prevent Sewer Overflows

There are a number of things that you can do to help prevent sewer overflows:

• Dispose of FOG and other non-flushable items properly. FOG and non-flushable items can clog sewer lines and lead to overflows.
• Reduce your water usage. Conserving water helps to reduce the amount of stormwater and sewage that enters sewer systems.
• Connect downspouts and sump pumps to storm drains, not sanitary sewers. Improperly connected downspouts and sump pumps can contribute to I&I and sewer overflows.
• Support investment in sewer system maintenance and upgrades. Sewer systems are complex and require regular maintenance and upgrades to prevent overflows.

What is WLSSD doing to address Sewer Overflows?

WLSSD, local municipalities, and utilities continually work to address sewer overflows through a variety of measures, including:

• Investing in sewer system maintenance and upgrades. This includes monitoring, repairing, and replacing damaged sewer lines, as well as improving the capacity of sewer systems to handle heavy rainstorms by building basins to temporarily store water during the event.
• Implementing green infrastructure projects. Green infrastructure projects, such as rain gardens and permeable pavement, can help to reduce I/I and storm water runoff.
• Educating the public about sewer overflows. Public education efforts help people to understand the causes and impacts of sewer overflows, as well as what they can do to help prevent them.

Past Overflows

Any overflows occurring in 2026 will be indicated on the map below: