Nearly a quarter of the world’s freshwater species are at risk of extinction: Report

(LONDON) -- Nearly a quarter of the world's freshwater species are at risk of extinction, according to new research.

A detailed extinction assessment of more than 23,000 species of freshwater fauna by the International Union for Conservation of Nature identified major threats from pollution, dams, agriculture and invasive species, according to a paper published Wednesday in the journal Nature.

The species studied included fish, decapod crustaceans -- such as crabs, crayfishes and shrimps -- and odonates, such as dragonflies and damsel flies. About 24% of those species are at risk of extinction, Catherine Sayer, lead of the freshwater biodiversity team for the IUCN, told ABC News.

"That means there are high to extremely high risks of becoming extinct in the future," Sayer said. "That's quite an alarming percentage."

Decapods have the highest percentage of species threatened at 30%, while 26% of freshwater fish and 16% of odonates are threatened, according to the analysis. Nearly 90 freshwater species have already been reported extinct, Sayer said.

Of the threatened species, 54% of studied species are thought to be affected by pollution.

Dams and water extraction are impacting 39% of the studied species, according to the paper.

"Dams completely block water courses, which means that species can't move downstream, and so they can't get to habitats that they previously used for breeding or feeding," Sayer said. "And that completely disrupts the lifecycle."

Land use change and associated effects from agriculture -- including the use of pesticides and herbicides -- are affecting 37% of the studied species, while 28% by invasive species and disease are impacting 28% of studied species.

Freshwater ecosystems are home to more than 10% of all known species and provide benefits such as nutrient cycling, flood control and climate change mitigation, the researchers said.

These species hold "intrinsic value" -- both ecologically and economically, Sayer said. Some species even hold cultural and spiritual value for indigenous groups, such is the case of the Atlantic salmon, Sayer said.

Other notable freshwater species that are threatened are the European eel, which is critically endangered, and several freshwater crustacean species in the Southeast United States, Sayer said.

Climate change is also threatening freshwater species and is expected to have more of an impact in the future, Sayer said. As global temperatures rise, it causes habitats to change, making it even easier for invasive species to thrive in ecosystems that were previous cooler, she added.

The analysis found that 18% of the freshwater species studied are threatened by climate change.

Since IUCN reassesses species every five to 10 years, researchers believe that if the analysis were repeated 10 years in the future that climate change would play a more prominent role in the decline of freshwater species.

"It's very much a threat that we see as intensifying, and it's it's getting worse with time," Sayer said.

The findings highlight the urgent need to address threats to prevent further species declines and losses and could help to inform future efforts to reduce the loss of freshwater biodiversity, the researchers said.

"We have about a quarter of species which are on their way to extinction if we don't do anything to stop it," Sayer said.

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