The Three Gorges on the Yangtze River 

not anymore

In Wuhan they placed the bridge at the spot where the river's thinnest. 1100 meters. Think about other parts.

There are many river battles in the past in Yangtz river, but not in Three Gorges. One of the famous river battle is the RED CLIFF battle in Hubei during Three Kingdom period; Another interested one is in Sichuan where a rebellion king had a river battle with the Ming army, and legend has it that the rebellion king has poured countless treasures into the river during the battles and there are even poems imply how big the treasures and where they are. And through the past 400 hundreds years, a lot of efforts have been made to excavate the treasures but were in vain. But the legend is truth, the 400 years old poems are also truth, in the past several years, massive excavating work have found tremendous gold, silver and other jewleries hidden under the river.

That depends on the soil type and the speed of flow. Look at the Amazon River, very few people live nearby and it's natural color is brown with sediment.