Remi Masson / European crayfish (Astacus astacus) in a lake. Alps, Switzerland, July.

Michel Roggo / Signal crayfish (Pacifastacus leniusculus), fighting for burrow built in the soft limestone lake bed, Lake Neuchatel, Switzerland, October. Photographed for The Freshwater Project.

Michel Roggo / Signal crayfish (Pacifastacus leniusculus), Lake of Neuchatel, Switzerland, October. Photographed for The Freshwater Project.

Paul Hobson / White-clawed crayfish (Austropotamobius pallipes) on riverbed, Staffordshire, UK. September.

Paul Hobson / White-clawed crayfish (Austropotamobius pallipes) on riverbed, Staffordshire, UK. September.

Michel Roggo / Signal crayfish (Pacifastacus leniusculus), fighting over burrow dug in soft limestone ground. Lake Neuchatel, close to Boudry, Canton of Neuchatel, Switzerland. October. Photographed for The Freshwat...

Michel Roggo / Signal crayfish (Pacifastacus leniusculus), a North American species of crayfish, introduced to Europe in the 1960s. Lake Neuchatel, close to Boudry, Canton of Neuchatel, Switzerland. October. Photo...

Cyril Ruoso / Signal crayfish (Pacifastacus leniusculus), non-native invasive species. On riverbed in woodland. La Cure river, Morvan, Bourgogne-Franche-Comte, France. May.

Cyril Ruoso / Signal crayfish (Pacifastacus leniusculus), non-native invasive species, on riverbed. La Cure river, Morvan, Bourgogne-Franche-Comte, France. May.

Cyril Ruoso / Signal crayfish (Pacifastacus leniusculus), non-native invasive species, on riverbed in woodland. La Cure river, Morvan, Bourgogne-Franche-Comte, France. May.

Paul Hobson / Signal crayfish (Pacifastacus leniusculus) on river bed near bridge, split level image. River Rivelin, Sheffield, England, UK. September 2018.

Paul Hobson / Signal crayfish (Pacifastacus leniusculus) displaying aggression with claws up, split level. River Don, Sheffield, England, UK. September 2018.

Paul Hobson / Signal crayfish (Pacifastacus leniusculus) displaying aggression with claws up. River Don, Sheffield, England, UK. September 2018.

Paul Hobson / White-clawed crayfish (Austropotamobius pallipes) on riverbed, split level image. Staffordshire, England, UK. October.

Nick Upton / White-clawed crayfish (Austropotamobius pallipes) collected from a well-stocked stream being released at an ARK site stream, safe from Signal crayfish (Pacifastacus leniusculus) and Crayfish plague, E...

Nick Upton / Alan Sumnall of GWT releasing White-clawed crayfish (Austropotamobius pallipes) collected from a well stocked location at at an ARK site stream, safe from Signal crayfish (Pacifastacus leniusculus) an...

Nick Upton / John Field placing White-clawed crayfish (Austropotamobius pallipes) in an inspection tray for sexing and health checks ahead of translocation to an ARK site, safe from Signal crayfish (Pacifastacus l...

Nick Upton / GWT team placing White-clawed crayfish (Austropotamobius pallipes) collected from a well-stocked stream in buckets for release at an ARK site, safe from Signal crayfish (Pacifastacus leniusculus) and...

Nick Upton / John Field and a GWT volunteer inspecting White-clawed crayfish (Austropotamobius pallipes) caught in a well-stocked stream to check their size, sex and health ahead of translocation to an ARK site, s...

Nick Upton / White-clawed crayfish (Austropotamobius pallipes) collected from a well-stocked stream in a bucket ready for release at an ARK site, safe from Signal crayfish (Pacifastacus leniusculus) and Crayfish p...

Nick Upton / Emma Settle of GWT disinfecting her boots before helping to release White-clawed crayfish (Austropotamobius pallipes) at an ARK site, safe from Signal crayfish (Pacifastacus leniusculus) and Crayfish...

Nick Upton / White-clawed crayfish (Austropotamobius pallipes) found in shallow stream by GWT team for translocation to an ARK site, safe from Signal crayfish (Pacifastacus leniusculus) and Crayfish plague, Englan...

Nick Upton / Large White-clawed crayfish (Austropotamobius pallipes) caught in a well stocked stream ahead of translocation to an ARK site, safe from Signal crayfish (Pacifastacus leniusculus) and Crayfish plague,...

Nick Upton / Very small White-clawed crayfish (Austropotamobius pallipes) beside a much larger one caught in a well stocked stream, with the smaller one not large enough for translocation to an ARK site, safe from...

Nick Upton / Large male White-clawed crayfish (Austropotamobius pallipes) with claspers visible under the tail, caught in a well stocked stream ahead of translocation to an ARK site, safe from Signal crayfish (Pac...

Nick Upton / John Field releasing a very large male White-clawed crayfish (Austropotamobius pallipes) back to a well-stocked stream where it was caught in case it proved too aggressive for safe translocation to an...

Nick Upton / GWT team processing White-clawed crayfish (Austropotamobius pallipes) in a well-stocked stream to check their size, sex and health ahead of translocation to an ARK site, safe from Signal crayfish (Pac...

Nick Upton / Richard Spyvee lifting a baited trap set for White-clawed crayfish (Austropotamobius pallipes) under license in a well stocked stream for translocation of healthy Crayfish to an ARK site, safe from Si...

Nick Upton / Richard Spyvee inspects a baited trap that has caught many White-clawed crayfish (Austropotamobius pallipes) under license in a well stocked stream for translocation of healthy Crayfish to an ARK site...

Jan Hamrsky / European crayfish (Astacus astacus), underwater, August, Europe, controlled conditions

Jan Hamrsky / European crayfish (Astacus astacus), underwater, August, Europe, controlled conditions

Jan Hamrsky / European crayfish (Astacus astacus), August, Europe, controlled conditions

Jan Hamrsky / European crayfish (Astacus astacus), underwater, August, Europe, controlled conditions

Ashley Cooper / Rare native White clawed crayfish (Austropotamobius pallipes) killed by an illegal chemical spill on the river Mint near Kendal Cumbria UK. June 2004

Ashley Cooper / Rare native White clawed crayfish (Austropotamobius pallipes) killed by an illegal chemical spill on the river Mint near Kendal Cumbria UK. June 2004

Ashley Cooper / Rare native White clawed crayfish (Austropotamobius pallipes) killed by an illegal chemical spill on the river Mint near Kendal Cumbria UK. June 2004

Will Watson / Scientist measuring a crayfish head and thorax of a non-native Signal Crayfish (Pacifastacus leniusculus), River Lugg SSSI, north Herefordshire, England, UK, August.

Will Watson / Scientist castrating Signal Crayfish (Pacifastacus leniusculus) during a control programme, River Lugg, SSSI, Herefordshire, England, UK, August 2017.

Remi Masson / Signal crayfish (Pacifastacus leniusculus) in a river. Haute-Savoie, Alps, France, October.

Remi Masson / Signal crayfish (Pacifastacus leniusculus) in a river. Alps, Haute-Savoie, France. October. Invasive species.

Remi Masson / Stone crayfish (Austropotamobius torrentium) in a small river. There are only 3 populations of this species left in France. Haute-Savoie, Alps, France, July.

Stephen Dalton / Signal crayfish (Pacifastacus leniusculus) seeking new habitat walking across land. Claws raised in defense, Rookery Wood, Sussex, England, UK. August.

Marie Read / Belted Kingfisher (Ceryle alcyon) female holding prey (crayfish) in her bill, New York, USA

Will Watson / White clawed crayfish (Austropotamobius pallipes) on gravel bed of stream, north Herefordshire, England, UK, October.

Will Watson / White clawed crayfish (Austropotamobius pallipes) on silty bed of stream, north Herefordshire, England, UK, October.

MYN / Dirk Funhoff / Stone Crayfish (Austropotamobius torrentium), Idar-Oberstein, Germany, January. meetyourneighbours.net project

MYN / Dirk Funhoff / Stone Crayfish (Austropotamobius torrentium), Idar-Oberstein, Germany, January. meetyourneighbours.net project

MYN / Dirk Funhoff / Stone Crayfish (Austropotamobius torrentium), Idar-Oberstein, Germany, January. meetyourneighbours.net project