Shade some cells in the grid so that the remaining white cells form a single connected area. The small numbers at the intersection of four cells give the number of shaded cells among them.
(Rules and example from WPC 2017 IB)
History of the puzzle
First appeared in Nikoli volume 110 (2005). Invented by 鴨川 ("Kamogawa"). Original title クリーク is transliteration of the word "creek."