Astacus (from the Greek αστακός, astacós, meaning "lobster" or "crayfish") is a genus of crayfish found in Europe, comprising three extant (living) species and three somewhat contested extinct species. These crayfish are found across Europe and live exclusively in freshwater, mostly inhabiting the bottom of lakes, ponds, and streams.

Due to the crayfish plague, crayfish of this genus have declined in many European regions, being replaced by the invasive North American signal crayfish, which carries the plague but is unaffected by it.

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