Hidden Depths of St. Louis: The River Des Peres Tunnel System
ST. LOUIS, USA (2025) – Beneath the scenic expanses of Forest Park lies a remarkable yet often overlooked network of tunnels, integral to the River Des Peres. This subterranean system encompasses over four miles of the river’s nearly 10-mile course, hidden well beneath the vibrant cityscape.
Originally constructed in the 1890s, the River Des Peres, once a natural waterway, turned into a receptacle for urban waste as St. Louis expanded. This issue became particularly pressing ahead of the 1904 World’s Fair, where the unattractive state of the river raised alarms among city officials and residents alike.
Sean Stone, Senior Public Affairs Specialist for the St. Louis Metropolitan Sewer District, explains the historical context: “Back in the day, people disposed of waste directly into local creeks; there were no wastewater treatment solutions. This neglect caused untreated sewage to flow into the River Des Peres, ultimately ending up in the Mississippi River.”
Efforts to conceal the river’s unpleasant odors began with a temporary covering. However, a more extensive, durable tunnel system was later established – a crucial component of St. Louis’ modern wastewater infrastructure.
A recent tour by Nexstar’s KTVI highlighted the Forest Park Junction Chain, a critical intersection where multiple tunnels converge, allowing for the integration of stormwater from Forest Park and wastewater flow.
“The city employs a combined sewer system where wastewater and stormwater share the same conduits, a common practice in many historical cities,” Stone noted. “This system directs waste through the River Des Peres, eventually leading to our Lemay Wastewater Treatment Plant.”
Despite its name, residents are cautioned against interacting with the waters or exploring the tunnels. “These are active sewage systems, carrying a mix from domestic sources, including sinks, showers, and toilets. There are significant risks, such as sewer gas and hydrogen sulfide, present in these tunnels,” Stone added.
Heavy rains can drastically raise water levels in minutes, posing serious hazards. Recent rainfall in St. Louis during the spring has led to overflowing tunnels.
Recognized as a National Historic Civil Engineering Landmark since 1988, the original construction of these tunnels featured wood imprints still visible today.
Stone elaborates on the evolution of engineering techniques: “Today, tunneling involves advanced machinery capable of boring massive holes, unlike the steam shovels and manual labor that crafted these structures a century ago. This tunnel is truly one of the great engineering achievements of its time."
The Metropolitan Sewer District is committed to maintaining the integrity of this historic system, with ongoing monitoring and upcoming plans to enhance it. Between 15 to 16 miles of new tunnels, reaching depths of up to 250 feet, are estimated to be in use by the late 2030s, boosting the River Des Peres System’s capacity by about 300 million gallons.
This ambitious project aims to further safeguard St. Louis’ wastewater management as the city continues to grow.