Imagine a bridge that doesn’t stand on tall legs but simply rests on the water like a giant boat. Bridges like this actually exist in Seattle, America! Now imagine that one day, one of them simply... sank. It didn’t break or collapse—it literally went underwater like a toy in a bathtub. This is a true story, and it can teach us something important.
Why the Bridge Couldn’t Stand on Legs
Seattle is home to a large lake—Lake Washington. A bridge needed to be built across it so people could quickly travel from one shore to the other. But the engineers—the clever people who figure out how to build all kinds of structures—ran into a problem: the lakebed was extremely soft. It wasn’t like rock; it was more like thick pudding or jelly, with a full 60 meters of silt! If they tried to drive tall concrete supports into it, the supports would simply sink into the muck.
So the engineers came up with a clever idea: what if the bridge didn’t touch the bottom at all? What if it simply floated on the surface of the water like a giant boat?
A Bridge-Boat Made of Concrete
To keep the bridge afloat, the engineers built enormous concrete boxes called pontoons. A pontoon is like a gigantic bathtub that is hollow inside, except that it is made of concrete and is as large as a house. The empty space inside is filled with air, so the pontoon doesn’t sink—just like a sealed plastic bottle stays afloat even if it is made from a heavy material.
Dozens of these pontoons were connected in a chain, creating a long bridge across the lake. One of them—the Lacey V. Murrow Memorial Bridge—was for a long time one of the longest floating bridges in the world!
The Night the Bridge Went Underwater
Now for the most interesting part. In 1990, workers decided to carry out some repairs on the old Murrow Bridge. To do this, they removed the covers from several pontoons—the very “boxes” that kept the bridge afloat. The covers were taken off, and then heavy rain began to fall nearby.
Rainwater poured straight into the pontoons, just as it would into an open bottle. The pontoons filled with water, became heavy, and simply sank to the bottom of the lake, taking part of the bridge with them! Fortunately, this happened at night, when there were almost no cars on the bridge, so no one was seriously injured. But Seattle residents woke up in the morning to discover that part of their famous bridge had disappeared beneath the water.
As the engineers who investigated the incident later explained, the disaster was not caused by a poor bridge design. It happened because, during the repairs, people forgot a simple rule: an empty box must remain closed, or it will fill with water and sink—just like any boat.
It’s like forgetting to close the valve on an inflatable mattress before taking it swimming in a pool. At first, everything seems fine, but then water starts leaking inside, and the mattress slowly sinks beneath the surface.
Here is a small table showing Seattle’s most important floating bridges:
| Bridge | Feature |
|---|---|
| Lacey V. Murrow Memorial Bridge | The first floating bridge; partially sank in 1990 |
| Homer M. Hadley Memorial Bridge | Built next to the older bridge to help ease traffic |
| Evergreen Point Floating Bridge | One of the longest floating bridges in the world; rebuilt in 2016 |
A Lesson People Still Remember
After the incident, the bridge was repaired and made even stronger. Today, Seattle’s floating bridges are monitored especially carefully: engineers regularly check that the pontoons are sealed and that water cannot get inside. People learned that even the smartest idea needs care, and that one small overlooked detail—such as an open cover—can lead to major problems.
I think this story is a wonderful reminder that life depends not only on big, brilliant ideas but also on paying attention to small details. Even the strongest bridge can “sink” if a simple rule is forgotten. And Seattle’s bridges today are a living reminder of that lesson: they still float on the waves of Lake Washington, only now under the watchful supervision of people who remember the history of their unusual floating city.
