Tour de France organisers will hope the tide is out on June 30 2018 when the opening stage of the race travels across the often submerged Passage du Gois in the Vendee region.
Next year's Grand Depart will begin on the island of Noirmoutier-en-l'Ile and immediately travel across the natural passageway to the mainland as part of the 195-kilometre opening leg.
Day one of the Grand Tour will travel down the Vendee coast and finish inland at Fontenay-le-Comte, before the peloton face a 185km route on stage two.
That will see the riders leave Mouilleron-Saint Germain for La Roche-sur-Yon, a classic Tour route that has not been used for a stage finish for 80 years and is expected to favour the sprinters.
A team time trial around the village of Cholet completes Vendee's hosting of the 2018 Grand Depart, the world's greatest cycle race leaving La Baule on stage four for the remaining two and a half weeks of competition.
Where the fourth challenge will finish is yet to be confirmed, with the full route set to be announced on October 17 at the Palais des Congres de Paris.