More than 4,000 freshwater species are on the brink of extinction

A new global study reports that nearly one in four freshwater species – over 4,000 of the 23,496 assessed – are threatened with a high risk of extinction.

The team evaluated fishes, dragonflies and damselflies, as well as crustaceans such as crabs, crayfishes, and shrimps.

Freshwater habitats cover less than one percent of Earth’s surface, yet they hold an outsize share of life and provide water, food, and flood control for billions of people.

The results warn that the natural systems keeping those services running are in trouble.

The research was led by Catherine Sayer, of the International Union for Conservation of Nature (IUCN).

Some freshwater species are bioindicators

The IUCN Red List classifies species by their extinction risk, giving decision makers a shared yardstick for urgency. In this assessment, those yardsticks extend across rivers, lakes, wetlands, springs, and aquifers.

Freshwaters support more than one tenth of known species, including about one third of vertebrates. That diversity helps cycle nutrients, stabilize shorelines, and cushion communities from storms and floods.

Scientists also rely on many freshwater animals as bioindicators, species whose health reflects the condition of the water itself.

When small creatures start to vanish, it is often the first hard sign that water quality and flow are slipping.

Uneven risks across species

Across the groups analyzed, the risks are uneven. Among decapods such as crabs, crayfishes, and shrimps, 30 percent are threatened, compared with 26 percent of freshwater fishes and 16 percent of odonates, the dragonflies and damselflies.

Threatened species are not spread evenly either. Concentrations are highest in the Lake Victoria basin in East Africa, Lake Titicaca in the Andes, Sri Lanka’s Wet Zone, and India’s Western Ghats.

Some of these waters hold many endemic species, which cannot be found nowhere else in the world. When a lake or spring declines, these local specialists have no second home.

Threats that tip the balance

Pollution, dams and water extraction, agricultural change, and invasive species dominate the picture. Overharvesting has pushed some species over the edge historically, and it still matters for a subset today.

“Prevalent threats include pollution, dams and water extraction, agriculture and invasive species, with overharvesting also driving extinctions,” noted Sayer.

“Most species do not have just one threat putting them at risk of extinction, but many threats acting together.”

Hotspots and hidden risks

Lakes, springs, and oases stand out for extinction records because species tied to these habitats cannot easily escape change. When a lake is altered or an invasive predator arrives, isolation becomes a liability.

Underground waters also carry more threatened species than many expected. In porous karst landscapes carved in limestone, small, range restricted populations face pollution and water drawdown with little buffer.

Rivers that once flowed freely now run through dams and weirs that break migration routes and alter downstream habitat.

The study links these engineering changes to risk, not as a single cause, but as a driver that stacks with others.

Common shortcuts miss the mark

Many governments use abiotic measures, numbers about water itself rather than species, to steer conservation.

Two familiar metrics are water stress and eutrophication, the buildup of nutrients that fuels algal growth.

The authors compared conservation planning based on threatened species with approaches that prioritize water stress from Aqueduct and nitrogen levels from the World Bank.

The abiotic approaches performed worse than random at capturing where the most threatened freshwater species actually live.

This matters because conservation dollars are limited. If planners rely on the wrong signals, they miss the places where help would count the most.

What can we do to help?

We must act where threatened species still hold on, and match actions to the real pressures on water.

That means curbing agricultural runoff, fixing sewage, and setting flows that mimic natural seasons.

Management should also treat invasive species and overharvesting as live problems. In places where hatcheries or introductions have altered fish communities, prevention beats cleanup.

Rethinking conservation maps

The analysis tested whether threatened tetrapods, the amphibians, birds, mammals, and reptiles, can stand in as surrogacy targets for freshwater animals.

At large scales, tetrapods can be useful guides for rarity weighted hotspots, but they miss many of the most range restricted freshwater species.

This mixed result points to a practical compromise. Use terrestrial data to sketch a big picture, then switch to freshwater species data to set priorities within basins.

In river basins with ancient springs, caves, or short headwaters, fine scale maps of freshwater species are non-negotiable.

Otherwise, well-funded plans for terrestrial icons will bypass the reaches that house the most vulnerable fish and invertebrates.

Lack of data for freshwater species

Roughly one quarter of freshwater species in the assessment lack enough information for a clear risk category. That uncertainty is highest in invertebrates, which means overall risk is likely underestimated.

Better monitoring can close that gap. Long- term surveys and tools like environmental DNA can reveal species that nets and traps miss, and they can spot declines early enough to act.

Communities depend on healthy rivers and wetlands for drinking water, food, and protection from floods. When species vanish, those services erode.

The study’s map is a chance to change course while there is still time. It shows where many small actions, spread across real watersheds, can add up.

The study is published in the journal Nature.

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