Office de Tourisme :
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The highest tides in Europe at Mont Saint-Michel :
The Tides are caused by the action of the heavenly bodies, principally the sun and the moon. When they are in line with the earth (in syzygy) the attraction is multiplied, announcing spring tides, this corresponds with the period of highest tides ; on the contrary, if the sun and the moon form a right angle (in quadrature), the attraction is reduced and we are in neap tides, the period of lowest tidal movement.
These phenomena are accentuated in Mont Saint-Michel bay, because with the rock being in the back of the bay, the sea doesn't reach the Mount during neap tides. On the other hand during spring tides, the sea reaches the Mount but only after 4 hours and 30 minutes after the start of the rising tide, about every fortnight.
For 2017 please subtract 5 minutes for the time of the high water and add 1 metre for the height.
In case of high tide reaching (a height of) 12.85 metres or more, the road might be temporarily underwater.
The highest tides take place 36 to 48 hours after the full and new moons. These indications are a rough guide only and can be affected to acertain extent by atmospheric conditions. The highest tides in continental Europe take place at Mont Saint-Michel, up to 15 metres difference between low and high water. During top of the spring tides, the sea goes out 15 kilometres from the coast and comes in again very quickly.
To observe the phenomenon of the rising tide, you must be present 2 hours before the times indicated on spring tide days.
The bay is extremely dangerous. Do not venture without a certified guide, including around the Mont-Saint-Michel.