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Arctic lakes and rivers are losing the ability to sustain unique Arctic life. Climate change and human development are driving changes to biodiversity that threaten the health of Arctic freshwater systems. But how do we know these changes are taking place, and what are the impacts?

Our Conservation of Arctic Flora and Fauna (CAFF) Working Group conducted the first circumpolar assessment of freshwater biodiversity across the Arctic. The resulting State of the Arctic Freshwater Biodiversity Report identifies changes and knowledge gaps in freshwater fish, aquatic invertebrates, and plants, highlighting what countries can do to improve the situation. The report is a first step toward more rapid detection, communication and response to trends in Arctic water quality and biodiversity. Here are the top five takeaways you need to know.

1) Climate change is one of the greatest threats to the unique biodiversity of Arctic freshwaters

Arctic lakes, rivers and wetlands are highly threatened by climate change and human development, which can alter the abundance of species and affect biodiversity on which many Arctic peoples depend.

The warming climate affects freshwater ecosystems in a number of ways, including increasing permafrost thaw, which can flood rivers with mud, sediments and nutrients, smothering species and disrupting ecosystems. Warmer water in Arctic rivers and lakes can also lead to an increase in overall biodiversity as southern species move north. However, the species that currently live in the Arctic will be at risk due to competition from non-native species. Continued warming pushes cold-water species to the brink, making local extinctions soon possible.

2) Regions with warmer climates and connections to the mainland have higher biodiversity

Patterns of biodiversity vary across the Arctic, but ecoregions that typically experience warmer temperatures and those that have connection to the mainland generally have higher biodiversity than those with cold temperatures (high latitude or altitude) or on islands far from continental mainland.

Inland lakes of Finland, Norway, Sweden and parts of the Russian Federation (known as the Fennoscandian region) are biodiversity hotspots for freshwater invertebrates and fish. Coastal lakes in Alaska are among the most diverse ecoregions for fish in the Arctic. However, lakes in northern Canada, Greenland, Iceland and Russia appear less diverse. This directly correlates with temperature patterns in the respective regions.

Biodiversity in mountainous ecoregions of North America and Fennoscandia is generally lower, likely due to harsh environmental conditions typical of these regions. Biodiversity is also lower on remote islands where movement and introduction of species can be limited. This is particularly evident in Greenland, Iceland, the Faroe Islands, Svalbard and Wrangel Island in the Russian Federation.

3) Temperature is the primary – but not only – driver for most elements in freshwater ecosystems

Climate, geographical connectivity, geology and smaller-scale environmental parameters such as water chemistry are also important drivers of Arctic freshwater biodiversity.

Biodiversity tends to decrease at higher latitudes, particularly above 68°N. This northward decline in diversity is strongly related to decreasing maximum summer temperatures. High-latitude lakes and rivers show differences in diversity and composition of fish, plankton, diatoms and macrophytes compared to lower-latitude systems.

As temperatures continue to increase, cyanobacterial blooms are expected to become more common. These blooms can produce powerful natural poisons to humans, wildlife and the environment. They can also cause harm to freshwater systems by blocking sunlight and stealing oxygen and nutrients that other organisms need to live. Lastly, cyanobacteria provide a poor food resource for invertebrate consumers, thereby ultimately reducing fish production.

4) Freshwater species have changed over the last 200 years, but that change is less dramatic in areas with more stable temperatures

Available long-term monitoring data indicate that freshwater biodiversity has changed less in areas where temperatures have been more stable. For example, shifts in the composition of algae in lake sediment over the last 200 years were weakest in eastern Canadian coastal ecoregions (e.g., northern Labrador and Quebec) where temperatures have historically been more stable with less evidence of warming.

On the flip side, long-term fish monitoring records from Iceland indicate declining abundance of Arctic char and increasing dominance of Atlantic salmon and brown trout since the 1980s. At the same time, increases in spring and fall water temperatures will likely affect spawning and hatching time of Arctic char.

5) More data are needed for a deeper look into Arctic biodiversity patterns

Existing and available data are not sufficient to describe biodiversity patterns in all ecoregions of the Arctic, and increased sampling is required to improve understanding of biodiversity change. Improved research coordination, standardized methods, emerging technologies, use of Traditional Knowledge and Local Knowledge and better community engagement are all ways to improve the ability to detect and report on significant changes in the Arctic.

Continuous monitoring and assessment of changes in Arctic freshwater biodiversity is necessary for the benefit of Arctic wildlife and current and future generations. Read the full report here.