How does drought impact freshwater biodiversity?
18th July 2025
People, understandably, worry that drought spells disaster for life in freshwater – after all, how can aquatic species survive without water? But many freshwater plants and animals can survive, or even need, periods of drought. While some – like fish – need water all the time, many freshwater species have lifecycles that are well adapted to periods of drying out.
However, prolonged drought caused by climate change poses a serious threat to freshwater biodiversity. The risks are increased because so much of the freshwater environment is fragmented and polluted.
The benefits of seasonal waters
Most of the globe’s freshwater network is made up of temporary waterbodies and around half of the world’s river network is believed to be seasonal, drying out for part of the year. In the UK, an estimated 30% of ponds are semi-permanent or seasonal – and while some may only dry out once every 10 or 15 years, others dry every year.
In hot and dry parts of the world, people are far more used to seeing temporary waters and recognise them as ‘typical’ freshwater habitats. These are less familiar to us in Britain because so many of our temporary waters have been drained – and because we assume, incorrectly, that in a wet country like ours, temporary water would naturally be rare.
Periodic drying out is not only beneficial to some animals and plants – including rare species – but can also have a positive impact on widespread species. For example, we sometimes design ponds that will dry more frequently to reduce the build-up of predators for Great Crested Newts.
- Tadpole Shrimp (Triops cancriformis) - one of Britain's most endangered animals - is a specialist of temporary ponds. Copyright Neil Phillips
The threat of frequent drought
While our research has shown that many freshwater species readily bounce back from occasional periods of drought, we know that excessively hot, dry weather year after year can bring more profound long-term changes to both standing and running waters.
These changes can be due to simple shifts in temperature and availability of permanent water, but more usually involve the complex, and sometimes unexpected, interactions between freshwater plants and animals.
For example, higher temperatures can lead to increased growths of algae which smothers aquatic plants, while increased water evaporation and lower flows can concentrate the damaging cocktail of pollutants that freshwater animals and plants often have to live in.
Although many freshwater species have evolved to survive periods without water, they are unlikely to thrive in polluted, fragmented freshwater landscapes. This is because there will be fewer clean and unpolluted habitats for plants and animals to spread into. Sensitive species will be rare in those landscapes because, once eliminated by drought, it will be much harder for them to recolonise.
- Many of the ponds Freshwater Habitats Trust surveyed in May and June 2025 were partially or fully dry.
Becoming more drought resilient
The good news is that there are positive steps we can take to help our freshwater wildlife cope with more frequent droughts and increasing temperatures.
To be more drought resilient and protect freshwater species, we need healthy and interconnected freshwater landscapes. In particular, we need as much clean and unpolluted water as possible. That is why we’re committed to building the Freshwater Network and bringing about a reset for freshwater.
The Freshwater Network includes the whole freshwater environment, but with a focus on small waters, such as ponds which collectively support more species than streams and rivers. Whether ponds are permanent or seasonal, these small waterbodies can help to make the freshwater environment more resilient to the impacts of climate change.
Carefully located new ponds which can be protected from pollution increase whole landscape freshwater biodiversity, reversing on-going declines caused by pollution, loss of habitat and climate change. Our own research and conservation work has shown that simply doubling the number of clean water ponds in an area can increase the resilience of freshwater communities to drought and other stresses across whole regions. Because they are biodiversity rich, ponds can also play a vital role in helping freshwater wildlife recover from drought.
Re-wetting landscapes and creating wetland mosaic habitats helps us to hold more water in the landscape, which can reduce the impacts of flooding as well as drought.
By protecting the remaining high-quality freshwater habitats and building out from these hotspots by bringing new clean water to the landscape, we can support freshwater wildlife in a rapidly heating world.
- New ponds created at Manor Farm, Buckinghamshire