Freshwater conservation has a mapping problem: rivers and lakes face pressures that land-focused biodiversity studies often miss. A new global analysis seeks to close that gap.
A new map of pressure on freshwater life
Researchers led by McGill University have assembled a global assessment of threats to freshwater species, identifying agriculture, dams and runoff among the most widespread pressures on rivers, lakes and wetlands. The study appeared in Science on October 29 and examined thousands of species rather than focusing only on water quality or human water use. Its conclusion is not that every waterway faces the same danger. Instead, different groups of animals experience different combinations of pressures, and those patterns vary sharply by region. The work is intended to help conservation planners identify where particular interventions may matter most.
Why freshwater needs its own assessment
Conservation research often emphasizes forests, grasslands and other terrestrial habitats. Freshwater ecosystems are connected to the surrounding land but respond to a distinctive set of disturbances, including river barriers, changes in water flow and pollution carried downstream. A species can be affected by activities far from the place where it is observed. A dam upstream may change sediment transport, while farming across a catchment can influence nutrient levels in a lake. Treating freshwater merely as a subset of terrestrial conservation can therefore miss important risks. The new analysis attempts to make those pressures visible on their own terms.
The scale of the dataset
The researchers used information from the International Union for Conservation of Nature’s Red List to examine 45 threats affecting 21,490 freshwater species. The groups included fish, amphibians, reptiles, mammals and odonates, the order containing dragonflies and damselflies. Combining species distributions with recorded threats allowed the team to develop a spatial view of where particular pressures are likely to occur. The numbers describe the scope of the analysis, not a claim that exactly 21,490 species are currently threatened with extinction. Threat exposure, conservation status and actual population decline are related but different measures.
Two hundred and twenty-five maps
The study produced 225 maps by examining the 45 threats across five major animal groups. These were then used to construct a cumulative view of pressure on freshwater biodiversity. That approach is more informative than a single global ranking because it preserves differences between taxa. A threat that is widespread for amphibians may be less important for aquatic mammals, while hunting can have a different spatial pattern from agricultural runoff. The resulting maps are analytical products built from available records and modeling. They should not be mistaken for direct field measurements of every river or a precise count of animals at each location.
Europe and Northwest Africa stand out
The researchers identified Europe and Northwest Africa as particularly heavily affected regions in the global analysis. These landscapes contain long histories of settlement, farming, water infrastructure and river modification. Multiple pressures can overlap in a single basin, leaving species with few unaffected habitats. A high mapped threat score does not mean every freshwater species in those regions is declining at the same rate. It indicates that the combination of recorded pressures warrants close attention. Conservation decisions will still require local evidence about populations, water conditions and which interventions are feasible.
Agriculture affects more than water clarity
Expanding farmland can remove wetlands, alter stream banks and fragment habitats. Fertilizers and other materials can enter rivers through runoff, changing nutrient balances and sometimes contributing to oxygen depletion. Irrigation can alter the timing and quantity of water flowing through a catchment. The study identifies agricultural expansion and intensification as major pressures for amphibians and odonates in particular. This does not mean farming is the only cause of freshwater decline. It means agricultural practices are among the most widespread drivers that conservation policy must address, often through cooperation with land managers rather than through protected areas alone.
Dams reshape river ecosystems
A dam can change a river’s flow regime, temperature, sediment movement and the ability of animals to migrate. Some species depend on seasonal floods to breed or feed, while others require connected routes between different habitats. Hydropower and water-storage infrastructure provide benefits to people, creating real trade-offs for planners. The new mapping helps show where river regulation may intersect with vulnerable species. It does not provide a universal recommendation to remove dams. Decisions about fish passages, environmental flows, restoration or infrastructure changes need engineering analysis and an understanding of local ecological conditions.
Threats differ among animal groups
McGill’s research summary reports that amphibians and dragonflies or damselflies are especially affected by agricultural activity, while hunting is more prominent among threats to some freshwater reptiles and mammals. These differences matter for policy. Reducing fertilizer runoff may help one group but do little to address direct exploitation of another. Likewise, a protected wetland may still be vulnerable if its inflowing water is polluted. Conservation strategies are more likely to work when they target the mechanism of harm rather than assuming all freshwater species need the same intervention.
A watershed is the useful unit
Rivers and lakes collect water from surrounding landscapes, making watershed boundaries valuable for understanding threats. The researchers describe estimating the probability that species within a sub-watershed are affected by particular pressures. This approach can reveal connections between upstream land use and downstream biodiversity that administrative borders obscure. A river may cross several districts or countries, but its ecological processes do not stop at those boundaries. Coordinated management can therefore be more effective than isolated projects. The maps provide a starting point for deciding where such coordination is needed.
What the maps cannot prove
A global map is a synthesis of available data, not a replacement for field surveys. Red List records vary in coverage and precision, and some species are better studied than others. The modeling can identify likely patterns of exposure, but it cannot establish that a particular dam caused a specific local population decline without additional evidence. It also cannot predict the success of a proposed restoration project on its own. The study’s value lies in directing attention and comparing risks at scale. Policymakers should combine its results with local monitoring, community knowledge and detailed ecological assessments.
Why freshwater biodiversity matters to people
Healthy freshwater systems support drinking-water supplies, fisheries, flood management and other services. Species contribute to food webs, nutrient cycling and the functioning of habitats on which communities depend. Losses can have consequences beyond the animals themselves, though the effects vary by ecosystem. McGill’s researchers emphasize that freshwater conservation is not solely a concern for specialists. A degraded watershed can create practical challenges for farms, cities and local livelihoods. Protecting biodiversity and improving water management are not always identical goals, but they often overlap in ways that justify integrated planning.
The challenge of overlapping pressures
A river basin may simultaneously experience pollution, water extraction, habitat fragmentation, invasive species and climate stress. Addressing only one factor may leave the system vulnerable to others. The study’s cumulative mapping is designed to reveal such overlap. It can help decision-makers distinguish a basin where runoff is the dominant concern from one where several different threats require a coordinated response. The difficulty is that policies can have unintended consequences: changing water allocation, for example, may affect agriculture and communities. Effective conservation needs to consider ecological outcomes alongside social and economic realities.
How conservation priorities could change
Conservation budgets are limited, so planners must decide where to act first. Maps showing species exposure to multiple threats can help identify places where interventions may protect many vulnerable populations or prevent irreversible damage. They can also highlight under-recognized freshwater areas that are not captured by broader terrestrial conservation priorities. The researchers describe their work as a baseline, not a final list of projects. Choosing a specific intervention still requires evidence about cost, feasibility, local governance and likely ecological benefit. The new dataset is most useful when it sharpens those choices rather than replacing them.
The global comparison is significant
The team also compared its freshwater results with earlier assessments of threats to terrestrial vertebrates. It found distinct spatial patterns and, overall, stronger mapped pressures on freshwater species. This supports the argument that freshwater biodiversity needs dedicated attention in international conservation frameworks. However, comparing two large datasets requires care because their methods and underlying records can differ. The study reports a systematic attempt to make that comparison fair. The policy lesson is not to neglect terrestrial ecosystems but to recognize that freshwater life may face risks that general biodiversity indicators fail to describe.
What researchers will do next
The next stage is to use the framework to identify particular species and locations where protection or restoration could make a measurable difference. That may involve finer-scale field data, assessments of river connectivity and evaluations of management options. The October 29 publication establishes a broad geographic baseline for those investigations. Its strongest contribution is showing that threats to freshwater animals are neither uniform nor adequately represented by land-based conservation maps. A more targeted response will depend on turning those insights into monitored actions, with results assessed over time rather than assumed in advance.
Frequently asked questions
How many species did the study examine?
The researchers analyzed 21,490 freshwater species across five animal groups, using IUCN Red List information.
Which threats were most prominent?
Agriculture, dams and agricultural runoff were among the leading global pressures, with effects differing among animal groups.
Does the study identify the exact cause of every local decline?
No. It maps likely threat exposure and patterns; local causal analysis and field monitoring remain necessary.
Source: McGill University research release, October 29, 2026. Journal: Science, DOI 10.1126/science.aeb7910.
