Dams on rivers are changing the flow of water, affecting the shape of estuaries like the Yangtze. By looking at different channels in the estuary, researchers found that dams are making the north channels smaller and the south channels bigger. This is because the dams are making the water flow differently, causing more erosion in some areas and more sediment buildup in others. To keep the main shipping channel working well, the north channel needs more water flow.