Looking north from the Van Buren Street Bridge, weeds grow from the concrete on the western edge of the Chicago River below a curving, glassy building at 300 S. Riverside Plaza.
What you can’t see from the bridge, and can really only understand from a kayak floating on the river, is that this section of concrete is a remnant from when the Chicago River was reversed in 1900.
That reversal was one of the massive feats of engineering that changed Chicago. The concrete is leftover from a tunnel through which part of the South Branch flowed, forming Chicago’s very own “sea caves.”
The caves are an isolated remainder along the built-up and modernized river banks. Other than in a kayak, there’s no way to get inside the ruin, but paddlers low enough on the water can duck their heads as they approach a steel girder that supports the concrete.
From the retaining wall under 300 S. Riverside Plaza, a pair of concrete-lined half-tubes overhead extend out about 15 feet. They end at sheer concrete walls, which are broken in places and let in daylight.
Paddle past the tubular vaults and you emerge into an open-air “room” with no ceiling. The space is framed on three sides by giant steel girders that run horizontally about a foot above the water’s surface.
How the caves are connected to the Chicago River reversal
The tunnel that forms today’s sea caves is part of a solution to the challenges of reversing the Chicago River.
The river was reversed for two reasons: sanitation and ship transportation.
In the 1890s, when the Chicago River flowed naturally into Lake Michigan, the river’s heavy industrial pollution was often carried out into the lake, contaminating Chicago’s drinking water. Making the river flow backward, as it now does, would mean keeping the sewage and drinking water separate.
But the reversal was also needed to carry large modern ships toward the Mississippi River, which meant widening and deepening the river downtown to provide the volume of water and current that broad modern barges needed.
But widening the river wasn’t always that simple, says Chicago geographer and historian Dennis McClendon. Just north of Van Buren, an elevated railroad “rolling lift” bridge, built just five years prior, sat on a supporting structure that extended into the river from the west bank. When tall boats would pass through, counterweights dropped down into pits and the bridge would roll up.
Those pits — where the sea caves are located now — were a barrier to widening the river. And because there was a streetcar tunnel below the river, the engineers couldn’t dig any deeper.
The solution devised by Isham Randolph, chief engineer of the project, was to build a tunnel below the pits that would run parallel to the river, on the west side of the bridge supports. This tunnel would hold water displaced by large boats, so that the water didn’t get pushed against the supports of the bridge. On top of the tunnel, the Pennsylvania Railroad tracks would run towards Union Station.
In 1961, this defunct railroad bridge was removed as part of a downtown beautification effort, but the water-level remnants of the bypass were left behind. Now, nearly 60 years later, this relic of the grand plan to reverse the flow of the Chicago River is hiding in plain sight.
Dennis Rodkin is a real estate reporter for Crain’s Chicago Business and Reset’s “What’s That Building?” contributor.