Cook County Reservoirs Store 13 Billion Gallons as McCook Hits Capacity for 6th Time in 2026
Updated
Updated · NBC Chicago · Jul 7
Cook County Reservoirs Store 13 Billion Gallons as McCook Hits Capacity for 6th Time in 2026
3 articles · Updated · NBC Chicago · Jul 7
Summary
More than 13 billion gallons of stormwater are now being held in Cook County’s Tunnel and Reservoir Plan after weekend rain, with officials calling it a record load for the system.
McCook Reservoir in Bedford Park holds over 3.6 billion gallons and is full, while Thornton near South Holland is at 94% with more than 7.4 billion gallons—the highest level there since it opened in 2015.
The Deep Tunnel system channels runoff and sewage through 110 miles of underground tunnels into three reservoirs, preventing overflows into rivers, neighborhoods and, in extreme cases, Lake Michigan.
Officials said the system is still containing the recent storms’ water, and with no major rainfall in the near-term forecast, treatment plants can begin processing and draining the reservoirs.
McCook has already hit capacity six times in 2026 versus five times in the previous five years combined, underscoring pressure on a system MWRD plans to expand to 17.5 billion gallons.
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Chicago’s Deep Tunnel System at the Brink: 13 Billion Gallons Captured, Flooding Risks Rise After July 2026 Storms
Overview
In early July 2026, Chicago faced intense rainfall that pushed the Deep Tunnel system to its limits. The Metropolitan Water Reclamation District's reservoirs and tunnels captured 13 billion gallons of stormwater, but key reservoirs like Thornton and McCook neared maximum capacity. With more rain forecasted, the system’s ability to protect the city was threatened, as its buffer for additional precipitation was greatly reduced. This heightened the risk of localized flooding and overflows, making the speed of water treatment and discharge critical for community safety. The situation highlights the urgent need for both infrastructure upgrades and adaptive strategies.