During the Great Chicago Flood of 1992 — 25 years ago this week — all eyes were on a swirling spot on the Chicago River’s North Branch, where an estimated 250 million gallons of water were pouring into railroad tunnels underneath downtown.

But Crain’s Chicago Business real estate reporter Dennis Rodkin tells Morning Shift the story of the billion-dollar flood actually started several yards north, at a quaint little wooden building at the east end of the Kinzie Street bridge — the bridge tender’s house.

The summer before the flood, contractors were hired to install new pilings (logs that keep boats from hitting the supports of a bridge) beneath the Kinzie Street bridge. But Great Lakes Dredge & Dock Co. workers realized pulling out the old pilings could uproot the little bridge tender’s house.

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To save the house they got permission to install the new pilings a bit further south — right on top of an abandoned freight tunnel, which eventually collapsed and formed that famous drain.

WBEZ’s Curious City recently dug into why those tunnels were there in the first place and found the story of the 1992 flood is “the most Chicago story ever,” complete with clout and corruption.

The story of the little house that started that story starts with two 19th century taverns.

Samuel Miller owned a bar on the east side of the North Branch and, according to Rodkin, may have been looking to poach customers from The Forks, a tavern on the west side of the river. So he built the first permanent bridge in Chicago, and consequently, the bridge tender’s house to go with it.

According to Patrick McBriarty’s book Chicago River Bridges, the bridge was replaced six times since it was completed in 1832, but remained one of the lowest in the city. It had to be lifted to let boats pass far more often than other bridges of the era, as many as 5,000 times a year.

That’s why it was the only remaining bridge tender’s house in the city that wasn’t automated by the 1990s. It was still staffed by a person at the time of the flood, so it had to stay put — and that’s why those pilings were moved that fateful day.

Audio available later today.