The Thornton and McCook reservoirs, designed to hold billions of gallons of rainwater, are nearly full.

As of Monday, July 6, the Metropolitan Water Reclamation District (MWRD) had stored over 13 billion gallons of stormwater in its deep tunnels and reservoirs following severe weekend storms that dumped 3.77 inches of rain on the Calumet Water Reclamation Plant alone.

The Thornton Composite Reservoir sits at 94 percent capacity with 7.3 billion gallons—the fullest it has been since opening in 2015. The previous high-water mark was 54.5 percent in 2019.

The McCook Reservoir reached full capacity on July 3 for the sixth time this year, holding another 3.4 billion gallons. Between 2021 and 2025, it filled just five times total.

“That’s not good. We got a lot of water,” said McCook Mayor Terrance Carr, also highway commissioner for Lyons Township, when told of the 94 percent capacity.

The TARP system—the Tunnel and Reservoir Plan, also known as the Deep Tunnel—consists of 110 miles of underground tunnels, each 8 to 33 feet in diameter and buried 150 to 300 feet below the surface. The system captures and stores stormwater until it can be treated at water reclamation plants and released.

If the reservoirs exceed capacity, water spills back into communities. Carr said recent storms already have caused flooding across the area.

“We’ve had enough flooding. Everybody flooded out,” Carr said. “Joliet Road in McCook flooded in a couple of spots. In the township, Willow Springs Road, Brainard Avenue, and Plainfield Road all had water problems.”

The MWRD warns that “if TARP is full and heavy rains continue, sewers can still overflow to waterways.”

The forecast offers brief relief: sunny skies are expected through Wednesday. But rain returns Thursday with a 60 percent chance of thunderstorms, isolated in the morning and more widespread by afternoon.

In the meantime, check your sump pump.

https://southwestregionalpublishing.com/2026/07/06/weekend-storms-fill-…