Estuaries, where rivers meet the sea, are influenced by tides and river flow. By studying 70 years of river data and using a computer model, scientists found that the strength of tidal currents and water levels in the Changjiang River estuary depends on how much water is flowing from the river. In the flood season, higher river flow leads to stronger tidal currents and water levels extending up to 90 kilometers. In the dry season, lower river flow results in different patterns, with tidal currents and water levels reaching up to 200 kilometers. This information helps us understand how rivers and tides interact in estuaries, which can be important for managing coastal areas.