Yorkshire Dales rivers and their wildlife 'particularly vulnerable to climate change'

As largely dry conditions look set to continue across Yorkshire, environmentalists are highlighting the importance of creating healthier and more resilient rivers to help wildlife cope with the impacts of droughts.

The Yorkshire Dales Rivers Trust (YDRT) has issued a call for investment to boost water levels, keep water temperatures lower and raise oxygen levels affecting fish, insects and other aquatic wildlife amid mounting pressures on the flora and fauna.

Aquatic ecologist Professor Jonathan Grey, of the Wild Trout Trust, said the consequences of rising temperatures had become quite stark in some areas of the Yorkshire Dales as most of them do not have much shade.

He said when temperatures rise the amount of water in the rivers shrinks. "The more exposed it is, the more the water is likely to warm up as the stones get exposed and heat up quicker."

Many tested watercourses in the Yorkshire Dales have been well above the ecosystem's ideal range of temperatures this summer.

Warmer water also reduces dissolved oxygen and affects overall water quality. Prof Grey said: "Some of the smaller becks that I’ve managed to survey have a bit of woodland cover and are notably cooler.”

He said he tested the temperature of the water to make sure it is within a safe range for the fish he would handle and about half of those without tree cover were too warm – above 18°C.

The leading ecologist added: “I’ve had to scratch around and find becks that are cool enough to work on. The mainstem Aire and the Wharfe have both been recorded for long periods above 20°C this summer. Even Malham Tarn has been above 20°C for six to eight days already.

"The lack of shade is a really big issue for our rivers in the Dales. Most of the species that live in the rivers are cold-adapted and prefer temperatures in the 10°C to 15°C range and have evolved over millennia to thrive in that temperature range. As soon as it goes above that they start to get stressed. Growth slows and it can affect reproduction."

The lack of tree cover beside the River Ure, near Hawes, leaves the watercourse more vulnerable to climate change.

Last year, an Environment Agency report revealed the average water temperature of the warmest summer month is projected to rise by about 0.6°C a decade. The projections indicated adult brown trout will be under threat from high summer water temperatures at almost all sites by 2080 as their upper growth and feeding temperature range of 19.5°C could be exceeded.

Prof Grey said trout often used ephemeral streams – temporary water channels that flow during or immediately after precipitation events – and because they laid their eggs over winter, it gave the fry sufficient time to hatch and migrate into bigger deeper channels.

"We’re going from quite extreme flood conditions in the winter to very dry conditions early in the spring for the last couple of years at least. It’s a worrying trend in that those fry may not be big enough to undertake a downstream migration.

"It highlights some of the other issues that we are trying to tackle across Yorkshire with the Great Yorkshire Rivers Partnership, which is focuing on removing redundant artificial barriers to better connect our rivers can move about in response to these sorts of changing conditions.”

Prof Jonathan Grey of the Wild Trout Trust surveying habitat on Oak Beck.

By 2043 the partnership aims to have addressed all artificial barriers negatively impacting fish populations in Yorkshire.

Removing barriers to fish migration gives wildlife access to a greater range of habitats, allowing fish to move into areas with more suitable water levels during dry periods. Meanwhile, riverside, or riparian, tree planting helps keep water temperatures lower by providing shade, whilst also maintaining oxygen levels and filtering pollutants that might otherwise wash into waterways.

Trees bring wider benefits too, helping to stabilise riverbanks, reduce erosion during high flows, and provide habitat for birds, insects and other wildlife.

YDRT says improving river health is one of the most effective ways of building resilience to increasingly frequent droughts and other extreme weather events. It works with farmers, landowners, communities and businesses across the region to protect and enhance rivers. This includes restoring natural river processes, planting trees along riverbanks, fencing rivers to prevent livestock access and associated pollution, and removing barriers such as weirs to allow fish to move freely through river systems.

"The dry conditions we’re seeing across Yorkshire are a reminder that climate change is no longer a future challenge, it’s happening now”, said Charlotte Simons, Senior Catchment Partnerships Manager.