Crayfish, Australia

Photograph by Carsten Peter , National Geographic

A foot-long crayfish dodges a hiker fording a stream in Australia 's Claustral Canyon. The color of these crayfish, called yabbies by canyoneers, remains a puzzle. In some streams they're orange. In others they're blue. The difference is due partly to water purity the blue ones are found in the clearest water.

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