High tides in Saint Malo
©High tides, Saint Malo|Yannick Le Gal

The largest tides in Europe

Because Brittany doesn’t do things by halves, the tides of Saint-Malo and Bay of Mont-Saint-Michel are among the biggest in Europe.
This captivating phenomenon offers breathtaking landscapes that you really must see at least once in your lifetime!


The tides are particularly renowned in the bays of Saint-Malo and Mont-Saint-Michel, where the difference between high and low tide can be over 14 metres (the equivalent of a four-storey building). On a scale of 20 to 120, the tidal coefficients here regularly reach 110. Victor Hugo described this unique phenomenon by comparing the speed of the tide with that of a galloping horse.

Twice a day, the coast offers up an amazing spectacle where the landscapes are constantly changing.


Low tide is equally as impressive, revealing lunar landscapes. As it ebbs, the water reveals an immense expanse of sand, radically transforming the landscape. This is the ideal time to take a net, a bucket and a spade and walk across the vast uncovered space to collect clams, razor clams, mussels, cockles, oysters, shrimps, etc. There is an abundance of shellfish.

But be careful! The strong currents and the speed at which the water rises require caution. Take advantage of this activity for a breath of sea air and enjoy the beauty of the landscape in front of you.


Let’s keep it simple to start with: tides are the result of the influence of two stars: the Moon and the Sun.
The sun is further away from the Earth, so its force of attraction is half that of the moon. As a result, most of the movement is linked to the Moon, which acts like a magnet on our oceans.
When an ocean passes in front of the Moon, it is attracted by it and the water level rises: this is the high tide. Conversely, when the Moon does not face the ocean, the water level drops: this is the low tide. The alternation of the tides occurs continuously and takes place approximately twice every 24 hours and 50 minutes.

High tides and tides of the century

Large tides (or spring tides) occur when the Moon and Sun are in alignment with the Earth and are strongly attracted to each other.
To know if it is a large tide, we measure its “coefficient”. The tidal coefficient has a value between 20 and 120.
The higher the coefficient, the higher the sea level (and therefore the tide is strong!). When it is higher than 90, it is called a high tide; above 118, it is called the tide of the century.
In reality, these tides do not occur every century (phew!). The latest one occurred in the Bay of Mont Saint-Michel on 21 March 2015 with a coefficient of 119 and a tidal range (i.e. the difference in water level between a high and a low tide) of 14.15 metres. For information, the next one will take place… in March 2033! Until then, patience, patience…