Atlantic Stream Crayfish

A. pallipes is olive-brown, with pale undersides to the claws (whence its specific Latin epithet pallipes, "pale feet"). It may grow to 12 cm (4.7 in) long, and adult sizes below 10 cm (3.9 in) are more common. It typically lives in rivers and streams about 1 m (3 ft) deep, where it hides among rocks and submerged logs, emerging to forage for food, and in lakes.

It is found from the easterly Balkan Peninsula to Spain and reaches its northerly limit in Great Britain, as well as Ireland (where it is considered introduced), where it is limited to some regions only: its highest densities are in chalk streams. A. pallipes is the only crayfish found in Ireland, occurring over limestone areas in rivers, streams, canals, and lakes. In France, A. pallipes is found in streams such as the Mornante and Sellon, two small tributaries of the Dorlay in the Loire department, where it is protected as a heritage species. It is also among the emblematic species of many French Natura 2000 sites as it tends to be less and less common in France while it used to be present in most rivers before North American crayfish species were introduced during the 20th century.

It has also been introduced to Corsica, Liechtenstein, and Portugal (from where it is now extirpated).

It is absent from more acidic waters and occurs in streams with a moderate flow alongside other freshwater invertebrates such as caddis fly, mayfly, and mollusc species. Trout and three-spined stickleback also occur in the same habitat. Tree roots and rocks in the banks provide shelter. Juveniles shelter in vegetation such as watercress and grass mats growing out of the bank.

Introduction of the invasive North American signal crayfish (Pacifastacus leniusculus) and red swamp crayfish (Procambarus clarkii): The former is a carrier of crayfish plague, an infectious disease to which it has resistance, while A. pallipes has none. Consequently, A. pallipes tends to be more and more restricted to upstream sections of small rivers and rivulets, which can be more prone to summer droughts, creating a domino effect for this fragile species.

Water pollution: Many local extinctions are caused by surface runoff of insecticides and of bleached, insufficiently treated, or illegal untreated wastewater.