An amphidromic point is a point within a tidal system where the tidal range is almost zero. They are the 3D equivalent of nodes in a standing wave pattern.
Amphidromic points occur because of resonance within oceanic basins and bays creating a standing wave pattern which rotates around the amphidromic (nodal) point. At the amphidromic point, there is almost no vertical movement, but further away there may be magnified tidal range, such as in the Bay of Fundy in Nova Scotia, Canada, where resonance between the tidal frequency and the natural frequency of the bay create extreme tides of up to 15 metres at its northernmost extremity.
Amphidromic points occur at Tahiti, near the Falkland Islands, and at several points around the coast of Britain.