One of the longest-running studies of streams in the world – the minute study of 14 brooks that tumble through a remote Welsh mountain landscape – has exposed a troubling loss of riverine wildlife.

Ecologists working on the Llyn Brianne Observatory project in mid Wales, which has been in operation for almost 40 years, have flagged up the disappearance and decline of invertebrates from the streams.

Steve Ormerod, a professor of ecology at Cardiff University’s school of biosciences, who has personally studied the 14 streams for 34 years, characterised the loss of freshwater organisms as a “hidden tragedy”.

He said: “Freshwater ecologists are seriously concerned at the plight of the world’s rivers, lakes and wetlands, and at the rate at which they’re losing plants and animals of many types.

“Yet, many people are unaware of this ongoing tragedy hidden beneath the water surface. Our results show that the buildup to species extinction can start in a subtle way, for example, where climate change causes numbers to decline before sudden disappearance.”

Facebook Twitter Pinterest Steve Ormerod: ‘Many people are unaware of this ongoing tragedy hidden beneath the water surface’. Photograph: Gareth Phillips/The Guardian

Ormerod said that while urban rivers were becoming more healthy, with animals and birds such as Atlantic salmon and dippers returning, rural streams and rivers were not doing as well.

“We need to step up action to prevent these losses and work of this type will help to inform the best approaches while providing a timely wake-up call.”

The data that the Observatory has gathered over the decades shows the loss or sharp decline of specialist organisms such as predatory flatworms, stoneflies and caddisflies.

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Their struggle does not attract the same headlines as the extinction of a spectacular mammal or bird, but their loss or decline may fundamentally change the nature of the streams they inhabit – and therefore affect other animals, such as the brown trout, that are to be found in the Llyn Brianne streams.

One species that has been lost is the flatworm Crenobia alpina, a cool-water stream predator. The creature vanished from Llyn Brianne and much of Wales when the temperature of the streams rose, although it has recently been found again in a cold stream that emerges from a cave in the Brecon Beacons.

The project originally grew out of a scheme to protect sea trout.

In 1973, the Llyn Brianne dam was opened at the headwaters of the river Tywi to supply water to much of south Wales. There was alarm that the dam would stop sea trout from reaching their breeding grounds, so an extravagant scheme was hatched to trap them, put them in lorries and transport them to streams on the other side of the dam.



After that, the Llyn Brianne Observatory project was launched in 1981 with its first focus on acid rain. The streams, which feed into the reservoir, were carefully chosen to represent a variety of types. Some trickle down from exposed hillside grazed by sheep, others plunge through the conifer forests, which are periodically harvested, and a few emerge from the remnants of oak woodland.

Over the years, hundreds of scientists have visited the 14 streams to take part in many experiments. There are some ingenious innovations. For example, a stainless steel cascade runs parallel to one of the streams.

Stream water is piped into it, allowing experiments to take place in the controlled environment of the cascade. There is no power source and if the temperature needs to be raised in the cascade researchers can pipe it through manure provided by one of the local farmers.

Despite Ormerod’s long spell studying the streams, his enthusiasm is undiminished. When he took the Guardian on a tour of the observatory, he pushed through thick undergrowth and scrambled down steep banks into streams with his net. The technique is to scrape the bottom of a stream with a boot and collect the creatures that are disturbed. A single scoop collects hundreds of organisms.

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Despite some of the data, Ormerod remains optimistic. He points out that acid rain was the big worry when the oservatory was launched, but that crisis has been tackled. “What that illustrates is that even if you are facing a major environmental problem, taking the right action can lead to solutions. That’s an incredibly hopeful message.”

He said the information the observatory was collecting would not halt climate change, but may lead to ways of adapting the landscape to mitigate the effects.

“There’s a whole set of invisible elements at play. The changing rainfall pattern, temperature changes, recovery from the past effects of acid rain. They are made real by the information that comes out of the streams and the organisms we monitor.

“What we are seeing is changes among rarer organisms and specialised organisms. They are starting to decline and that’s clearly consistent with the signals of climate change effect you see more broadly across the world. I think that early warning is an important one for us to see and heed,” Ormerod said.