In some river mouths and estuaries the incoming high-tide wave crest overtakes the preceding low-tide trough. This results in a wall of water proceeding upstream, and is called a __________.

Correct Answer: Option C — bore

Per Bowditch, a tidal bore is a steep, forward-moving wall of water produced when an incoming high-tide wave crest overtakes a preceding low-tide trough in shallow river mouths or estuaries. This phenomenon creates hazardous turbulent conditions for unmoored vessels.