A quarter of freshwater species are at risk of extinction. What factors have made them vulnerable?

Throughout its history, Earth has become home to an astonishing number of species: some have long since gone extinct, while others continue to thrive today. However, scientists have now made a new alarming discovery: nearly one in four species of freshwater fish, crustaceans, and dragonflies are under immense pressure and may soon disappear from the face of the Earth, reports Daily Mail.

According to the study, the main threats to these species are:

• chemical pollution;
• sewage pollution;
• excessive water extraction;
• invasive species.

A global assessment of freshwater animals was conducted using the Red List of Threatened Species by the International Union for Conservation of Nature (IUCN). Scientists focused on assessing the extinction risk of 23,496 species of freshwater fish, dragonflies, crabs, crayfish, and shrimp. The results of the study were published in the journal Nature and showed that 24% of freshwater animals, at least 4,294 of the assessed species, are currently at high risk of extinction. Pollution, primarily from agriculture and forestry, has affected more than half of the threatened species.

The analysis results also indicate that the habitats of freshwater species are suffering from land repurposing for agriculture, water extraction, and dams that block fish migration. At the same time, overfishing and the introduction of invasive non-native species particularly contribute to extinction.

It is noteworthy that rivers, lakes, streams, and freshwater wetlands are actually key habitats, supporting more than one-tenth of all known species, including one-third of vertebrates and half of all animals. Interestingly, they cover only about 1% of the Earth's surface.

Observations indicate that 35% of the world's wetlands were lost between 1970 and 2015. In comparison, this is three times faster than forest loss. Scientists have also found that 37% of major rivers longer than 1,000 kilometers no longer have free-flowing water along their entire length.

The team also discovered that the highest number of endangered species currently inhabit Lake Victoria—the largest lake in Africa, Lake Titicaca in South America, the wetlands of Sri Lanka, and the Western Ghats of India.

The diversity of freshwater species provides essential services such as flood control, climate change mitigation, and nutrient recycling, as well as supporting the culture and livelihoods of billions of people around the world. However, until now, scientists had not conducted a comprehensive analysis of the extinction risk faced by these species.

The assessment revealed that among all studied groups, crabs, crayfish, and shrimp are at the highest risk of extinction: 30 percent of these species are threatened, followed by 26 percent of freshwater fish species and 16 percent of dragonflies and damselflies.