10:30 a.m. Storm Update: MWRD’s TARP systems manages heavy rainfall

July 4 2026

The Metropolitan Water Reclamation District of Greater Chicago (MWRD) has captured billions of gallons of stormwater that have fallen across Cook County during multiple waves of storms. According to the National Weather Service, the latest storm event had rainfall amounts that ranged from approx. 3 inches at O'Hare International Airport, approx 2 inches at Midway International Airport, and nearly 2.5 inches in southern Cook County.

The MWRD operates the Tunnel and Reservoir Plan (Tunnel and Reservoir Plan (TARP) | MWRD), which is currently holding more than 10 Billion Gallons of water.

· The McCook TARP system serves central Chicago and 36 municipalities and is approximately 98 percent full with over 5 Billion Gallons captured.

· The Calumet TARP systemserves the south side of Chicago and 13 south suburban municipalities and is approximately 61 percent full with over 5.4 Billion Gallons captured.

The McCook TARP system has filled 6 times this year. For context, the McCook TARP system filled 5 times cumulatively between 2021 and 2025. Before storms, the MWRD lowers the levels of the Chicago Area Waterway System by diverting more water at its Lockport Powerhouse to provide added capacity in local waterways. The MWRD called for an Overflow ActionAlert Friday, urging area residents to conserve water to provide more capacity in sewers and local infrastructure to take on the influx of rain. With more rain in the forecast, the Overflow Action Alert remains in effect.

Receive direct Overflow Action alerts via text

Applications are now open for municipalities and local government entities to partner with the MWRD on four stormwater management programs designed to mitigate community flooding throughout Cook County. More information can be found at mwrd.org/stormwater/partnerships.

Visit these links for more information about the MWRD, Stormwater Management, TARP and how to help reduce flooding and protect water quality.