Saint Marcellus' flood or Grote Mandrenke (Low Saxon: /ɣroːtə mandrɛŋkə/; "Great Drowning of Men") was a massive southwesterly Atlantic gale (see also European windstorm) which swept across the British Isles, the Netherlands, northern Germany, and Denmark (including Schleswig/Southern Jutland) around 16 January 1362, causing at minimum 25,000 deaths. The storm tide is also called the "Second St. Marcellus flood" because it peaked 17 January, the feast day of St. Marcellus. A previous "First St. Marcellus flood" drowned 36,000 people along the coasts of West Friesland and Groningen on 16 January 1219.
An immense storm tide of the North Sea swept far inland from England and the Netherlands to Denmark and the German coast, breaking up islands, making parts of the mainland into islands, and wiping out entire towns and districts, such as Rungholt, said to have been located on the island of Strand in North Frisia, Ravenser Odd in East Yorkshire and the harbour of Dunwich.
This storm tide, along with others of like size in the 13th century and 14th century, played a part in the formation of the Zuiderzee, and was characteristic of the unsettled and changeable weather in northern Europe at the beginning of the Little Ice Age.