The Han River Is Huge. So Why Can Boats Still Run Aground?

When you stand beside the Han River in Seoul, one thing is hard to miss: it is enormous.

At its widest, the Han stretches about three-quarters of a mile (1.2 km) across Seoul. The river runs about 26 miles (41.5 km) through the city. Seoul's own figures describe it as roughly five to six times wider than the Seine in Paris and the Thames in London.

So a natural question comes to mind:

If the Han River is that wide, how can a boat possibly run into trouble because the river is too shallow?

The answer is surprisingly simple.

A wide river is not necessarily a deep river.

And for a boat, the width of the entire river is not nearly as important as the depth of the water along the route it actually uses.

A river is not a giant swimming pool with the same depth everywhere. Its riverbed rises and falls, and sediment and other material can accumulate in particular places. A vessel can have plenty of water around it and still encounter a shallow area directly beneath its hull.

This is one reason the Han River Bus has required detailed attention to its navigation route.

In November 2025, a Han River Bus became stuck on the riverbed. Before full-route service resumed on March 1, 2026, Seoul conducted a detailed depth survey along an 8.9-kilometer (5.5-mile) section between the Apgujeong and Jamsil terminals. Areas where sufficient depth had not been secured were dredged, and underwater debris was removed. Seoul also installed a system designed to help prevent vessels from leaving their designated route.

The importance of water depth can also be seen at Seoul Forest Pier. Before the pier opened in June 2026, the city widened the navigation channel from 60 meters (197 feet) to 100 meters (328 feet) and dredged the route to secure a depth of 2.5 meters, or about 8.2 feet.

Notice the wording: not the entire Han River, but the navigation channel.

That distinction matters.

A river can be hundreds of meters wide, yet a boat still needs a sufficiently deep and safe route through it.

And Seoul's cruise boats provide another example.

On March 28, 2026, a Han River cruise vessel stopped near Banpo Bridge. Seoul's investigation found that the vessel had a draft of 2.2 meters, or about 7.2 feet. The city said the vessel's relatively deep draft required particular attention to local water depth and tidal conditions. The vessel had also left its normal operating route between Dongjak Bridge and Banpo Bridge.

In other words, even a sightseeing boat cannot simply go anywhere on a river just because the river looks enormous.

The vessel's draft matters.

Draft is the distance from the waterline to the lowest part of a vessel's hull. The deeper a vessel sits in the water, the more water it needs beneath it.

This makes the Han River an interesting comparison with other famous city rivers.

Consider Paris.

The Seine is dramatically narrower than the Han. Within Paris, the river ranges from about 98 feet (30 meters) wide near Quai Montebello to about 656 feet (200 meters) near Pont de Grenelle. The City of Paris gives its depth within the city as approximately 11 to 19 feet (3.40 to 5.70 meters).

So a river can be much narrower than the Han and still have substantial depth for navigation.

London's Thames tells a different story.

Much of the Thames around London is tidal. The Port of London Authority explains that depths on the tidal Thames are measured from a chart datum, and the actual depth at a particular moment depends on the current tide level. In simple terms, the charted depth and the tide level together determine how much water is actually beneath a vessel.

That means a boat navigating the Thames cannot simply ask:

"How deep is the Thames?"

It also has to ask:

"How deep is it right now?"

The three rivers therefore offer three very different ways of thinking about a city river.

Seoul has an exceptionally wide river.

Paris has a much narrower river with substantial depth through the city.

London has a tidal river in which the available water depth changes with the tide.

But all three have something in common.

Boats cannot simply go wherever they want.

They need navigable water.

That is why the riverbed matters. So do the route, water level, vessel size and the depth of water beneath the hull.

And this brings us back to the Han River.

From a bridge or a riverside park, the Han looks like one enormous body of water. It is easy to imagine that a boat has almost unlimited room to move.

From the wheelhouse of a boat, however, the river looks different.

It is a route.

And that route has to be measured, marked, maintained and respected.

Perhaps that is the more interesting way to look at the Han River.

The question is not simply:

"How wide is the Han River?"

It is:

"Where, exactly, is the water deep enough for a boat?"

A river can be enormous and still have places where navigation requires careful attention.

And that is one of the things we cannot see from the riverside.