In areas where high tide is common, what phenomenon can occur when the tide sweeps up a river?

The occurrence when the tide sweeps up a river is known as a tidal bore. This phenomenon happens in certain rivers where there is a significant difference between high and low tide, causing a surge of water to flow upstream against the river's current as the tide rises. It creates a visible wall of water that travels upriver, often producing churning waves and sometimes causing dramatic changes in the river’s water level and flow. Tidal bores can be spectacular and are often the subject of interest for nature enthusiasts and researchers alike.

Understanding this phenomenon involves recognizing that it is typically associated with rivers that have a narrow estuary and a large tidal range. It differs from other tidal phenomena, such as tidal surges, which are mostly related to storm surges and the impact of weather conditions on sea levels.