MILWAUKEE - The Milwaukee Metropolitan Sewerage District (MMSD) announced on Friday, April 24, that the combined sewer overflow from severe weather in southeast Wisconsin last week was estimated at 2.7 billion gallons.
2.7 billion gallons released
By the numbers:
A news release from MMSD says discharges began on April 14 at approximately 8:24 p.m. All combined sewage overflow discharges wrapped up by 2 p.m. on April 19. The combined sewer overflow lasted for a total of 113.6 hours – or nearly five days.
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For comparison, in August 2025, the combined sewer overflow was 5 billion gallons. The August overflow was the largest reported by MMSD in 31 years.
Reason for overflow
What we know:
Officials said in the Friday news release that "repeated intense rainstorms on already saturated ground overwhelmed the conveyance system and inline storage system (ISS), forcing combined sewer overflow discharges." Officials went on to say MMSD closed the combined sewer gates to the ISS to reserve the remaining capacity for separate sewage and to prevent basement backups.
Preventing another discharge
What's next:
The District’s 10-year investment plan calls for $2.1 billion in improvements to regional water reclamation facilities and sewers to reduce the risk of overflows and basement backups.
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Part of that spending includes the Private Property Inflow and Infiltration Reduction Program throughout the service area. The plan also calls for additional wetland protections through MMSD’s Greenseams program which is currently at more than 5,400 acres of land that can capture and store more than 3 billion gallons of rain and melting snow.
The Source: Information in this post was provided by MMSD.