Option 1: A water spout - This is not the correct answer. A water spout is a tornado that forms over a body of water. It is not related to the meeting of a strong tidal current and river flow in river estuaries.

Option 3: An ebb-tide - This is not the correct answer. An ebb-tide refers to the outgoing or receding tide. It is caused by the gravitational pull of the moon and sun, and not specifically related to the meeting of a tidal current and river flow.

Option 4: A flood-tide - This is not the correct answer. A flood-tide refers to the incoming or rising tide. It is caused by the gravitational pull of the moon and sun, and not specifically related to the meeting of a tidal current and river flow.

Correct Answer: 2. A tidal bore - This is the correct answer. A tidal bore is a large wave that forms when a strong tidal current meets a river flow in some river estuaries. The collision of these two forces creates a powerful wave that travels upstream. Tidal bores can be observed in various locations around the world, and they can vary in size and strength depending on the specific conditions of the estuary. The