Freshwater habitats have low salt or salinity levels, typically less than 0.5 parts per thousand (ppt). They are supplied by various sources of freshwater, including rivers, streams, lakes, ponds, wetlands, and groundwater. They generally have higher dissolved oxygen levels compared to marine habitats. Their nutrient levels can vary widely but are often nutrient-rich due to the influx of organic matter and nutrients from terrestrial sources. Freshwater habitats often serve as an interface between aquatic and terrestrial ecosystems, creating unique transitional zones like wetlands and riparian areas. They support a wide range of biodiversity, including various species of microorganisms, fish, snails, worms, turtles, frogs, birds, mollusks, insects, algae, and aquatic plants. Unfortunately, freshwater habitats are often heavily impacted by human activities, including agriculture, urban development, dam construction, and pollution, which can have detrimental effects on the ecosystem.
The freshwater biodiversity of Mauritius is contained within 92 rivers and 232 rivulets, several manmade reservoirs, natural lakes and marshy areas. The island of Rodrigues has been divided into 20 major river basins and 10 minor ones, which have been for the most part that has dried up.
18 species of fish and 10 crustacean species were recorded in the main rivers of Mauritius according to the survey by Association Réunionnaise de Développement de l’Aquaculture (ARDA) in 2003.Three endemic crustacean species were also inventoried: Cardina mauritii, Cardina spathulorostris and Cardina richtersi (petite chevrette). However, most of those species are few in number.
Many of the watercourses in Mauritius become overgrown with invasive plant species have infested about 95% of riverbanks.
Freshwater resources are threatened by dumping of solid wastes in rivers, heavy use of agrochemicals in nearby agricultural fields, sewage disposal, and backfilling of coastal wetlands.
