Astacus (from the Greek αστακός, astacós, meaning "lobster" or "crayfish") is a genus of crayfish found in Europe and western Asia, comprising three extant and four extinct species. Due to the American crayfish plague, crayfish of this genus have been almost wiped out in Europe and have in many European countries been replaced by the North American signal crayfish, which is often more resistant to the plague.