Around one fifth of known crab species are restricted to freshwater habitats, making up 1,280 species. A comprehensive assessment of these species, coordinated by Dr Neil Cumberlidge at Northern Michigan University and the IUCN SSC Freshwater Crabs & Crayfish Specialist Group, was completed in 2009 ( Cumberlidge et al. (2009) Biological Conservation 142: 1665-1673) .
Freshwater crabs are found in rivers, streams, waterfalls, wetlands, karsts and caves and are restricted to the tropical regions of the Americas, Africa, Asia and Australasia. They are important indicators of water quality as they have low tolerance to polluted or otherwise impure water, contribute between 88% and 94% of the biomass of freshwater invertebrates of tropical freshwater ecosystems and play important roles in nutrient cycling within their habitats.
In the 2009 assessment of freshwater crabs, it was estimated that almost one third of all species were considered to be at risk of extinction.The majority of threatened species are semi-terrestrial species that are living in habitats subjected to deforestation, pollution and alterations in water drainage.