The opening and closing dates of the season are determined annually by the waterway administration to accommodate the weather, water flow and ice[2] conditions as well as the transportation demands.
[3] The term is also frequently used to designate number of days per year with easy navigation.
[5] In Ancient Greece, the navigation period on the Mediterranean Sea lasted while the Pleiades star cluster was visible[6] (May to November).
Maritime law of Hanseatic League already in the 13th century stated that the ships must remain in the winter ports after St. Martin's Day (November 11).
By the 15th century more detailed laws allowed sailing on the Baltic Sea from Cathedra Petri (February 22) to St. Martin's Day.