A tidal bore (bore = crest or wave) is a natural phenomenon which is seen in a very few parts of the world. The Bay of Fundy is particularly noted for its extremely high tides, the highest in the world, and for its tidal bores. The Bay of Fundy is bordered by Nova Scotia and New Brunswick in Canada and Maine in the USA.

A tidal bore is a wall of water that moves up certain low-lying rivers due to an incoming tide. Tidal bores form when an incoming tide rushes up a river, developing a steep forward slope due to resistance to the tide's advance by the river, which is flowing in the opposite direction. Thus we have the phenomenon of the river changing its flow before your very eyes, flowing in OVER the outgoing river water.

The height of the tidal bore increases with the range of the tide and may very in height from just a ripple to several feet.