Water in lochs and reservoirs in Scotland have undergone "rapid and extensive climate change driven warming" in recent years, a new report has revealed.
The report by Centre of Expertise for Waters (Crew) found that 97 per cent of monitored lochs and reservoirs had increased in temperature over a four-year period from 2015 to 2019.
The majority warmed by up to 1C per year during the period while nine per cent rose by more, and some by up to 1.3C.
Changes to the temperature risk harmful algal blooms developing, which could restrict their use for recreation and water supply, and as a safe habitat for wildlife, researchers claim.
It is expected that waters in the south and east of Scotland are expected to warm the most at first, but this climate-related impact will reach all parts of the country by 2040.
Mairi McAllan, Environment Minister, said: "This important research provides yet more worrying evidence of the risks of harm from climate change on Scotland’s water environment.
"It is vital that we do more to mitigate those impacts, to seek to reduce the pace of warming but also to adapt to it.
"We have committed £243 million since 2015 through the Agri-Environment Climate Scheme to support land management practices which protect and enhance Scotland’s natural heritage, improve water quality, manage flood risk and mitigate and adapt to climate change.
"Research like this will be hugely valuable in informing the development of policy solutions and measures to mitigate and adapt to climate change, and also protect, restore and enhance these vital natural assets."
So-called Lake heatwaves, short periods of extremely high water temperatures, are likely to increase over time, according to he report.
A rise in heatwaves is "likely to push aquatic ecosystems beyond the limits of their resilience, posing a threat to their biodiversity and related benefits they provide to society."
The study says that average April to September air temperatures are projected to rise by about 2.5C between 2020 and 2080.
Dr Linda May, a freshwater ecologist from UK Centre for Ecology & Hydrology and lead author of the report, said: "This research has shown, for the first time, that climate change is already warming our lochs and reservoirs in Scotland, and that this trend is likely to continue.
"It provides early warning of the potential impacts of climate change on biodiversity, water supply and recreational use, and highlights the need for mitigation measures to be put in place as quickly as possible."
The Crew report makes a number of recommendations to address the impacts of warming in the immediate term.
These include reducing the amount of phosphorus and nitrogen entering lochs and reservoirs from their catchments, because these are the main driver of algal blooms.
Sources of these plant nutrients, present in synthetic fertilisers as well as human and animal waste, include farm runoff and waste water discharges.
Actions such as the creation of buffer strips and constructed wetlands, are already under way in many catchments across Scotland aimed at reducing nutrient inputs.
NatureScot Freshwater and Wetlands Advice Manager, Iain Sime, said: "Scotland, like the rest of the world, is facing an unprecedented climate emergency. The findings of this comprehensive review are stark, demonstrating the impact that climate change is already having on our freshwater lochs and reservoirs, and their biodiversity.
"The need for urgent action is clear, and at NatureScot we are using the £65 million Nature Restoration Fund to prioritise efforts that support the conservation of our lochs and ponds."
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