SCOTLAND's lochs and reservoirs need a 'clean-up' as climate change could make them unsafe for wildlife, new research has warned.

A new report says urgent action is needed to curb a trend which is causing a rapid and extensive warming of the watercourses with risk of a rise of harmful algal blooms which could restrict their use for recreation and water supply, and as a safe habitat for wildlife..

The report produced for CREW, Scotland’s Centre of Expertise for Waters, says that risks to water quality and biodiversity are expected to rise with projected higher air and water temperatures over the coming decades.

The report shows that 97 per cent of monitored Scottish lochs and reservoirs increased in temperature between 2015 and 2019.

While most of these standing waters (88% ) warmed by 0.25°C to 1.0°C per year over this period, nine per cent increased by more than that.

The analysis reveals that water temperature at Loch Sgamhain (Loch Scaven), at the head of Glen Carron near the source of the River Carron in Wester Ross, warmed by almost 1.3°C a year - the highest increase among the Scottish lochs and reservoirs monitored.

Also registering high temperature rises over of over 1C were Loch Achray and Loch Lubnaig, small freshwater watercourses near Callander in Stirlingshire and Loch of Girlsta, the deepest in Shetland at about 65ft deep in places,  which is home to a unique sub-species of fish native only to Shetland - the slender char.

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Loch Achray

With water warming at a faster rate than climate, a projected increase in air temperature of 2.5°C in Scotland between 2020 and 2080 would result in a 3°C rise in lochs and reservoirs over that period.

Researchers from the UK Centre for Ecology and Hydrology warn that warming and changes in rainfall patterns associated with climate change increase the risk of outbreaks of harmful algal blooms, which outcompete other freshwater plant species and produce toxins that can affect animals and people.

They say this would"restrict the use of Scottish lochs and reservoirs for recreation and water supply, and as a safe habitat for wildlif"e.

The researchers' report, which aims to provide evidence to help regulatory and conservation agencies, water managers and policymakers plan future strategies to mitigate, and adapt to, climate change, also warns that high levels of phosphorous and nitrogen entering the watercourses need to be curbed.

It recommends cutting the amount of phosphorus and nitrogen entering lochs and reservoirs from their catchments, because these are the other main driver of algal blooms.

These 'nutrients' are present in synthetic fertilisers as well as human and animal waste, and sources of pollution in lochs and reservoirs include farm run-off and waste-water discharges.

The report says targets for the regulation of these 'nutrients' may also need to be reviewed in the light of climate-driven warming.

It is feared 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.

Freshwater ecologist Dr Linda May (below) of the UK Centre for Ecology and Hydrology, the lead author of the report, says: “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.

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"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.”

So-called Lake heatwaves, short periods of extremely high water temperatures, are likely to increase over time, according to the 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 authors also recommend further monitoring and research to improve our understanding of climate impacts on the complex functioning of lochs and reservoirs.

They say of particular interest is when those ecosystems and their biodiversity are likely to reach crucial ‘tipping points’ beyond which there may be no return.

Further research by CREW this year is expected to help address those questions.

Environment minister Mairi McAllan 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."