Imagine, for a moment, a wild salmon swimming in the ocean. She has been in the Norwegian Sea for two years, feeding on capelin, shrimp and sand eel to build up her size, energy and ability to produce healthy eggs. She has been lucky to avoid the fishing boats at sea and has managed to escape being ravaged by bacterial diseases and parasites such as sea lice.
Now, in early spring, she is overwhelmed by a genetic instinct to return to breed in the river in which she was born. She swims 2,000km towards the coastal edge of Ireland and enters the mouth of her estuary. The elevated nutrients have caused excessive algae growth, depleting the water’s oxygen, but still she manages to continue into the freshwaters of her natal river, dodging predators such as otters along the way.
The river’s water temperature is slightly elevated from climate change – salmon become stressed above 20 degrees – but she swims on up the river, against the current, towards the headwaters, where she will need to find cool, clean, oxygen-rich waters with plenty of clean gravel to dig a nest and lay her eggs.
And then, having survived this epic, dangerous journey, just a short distance from being able to breed, she hits a concrete wall.
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It could be a hydroelectric dam, a sluice or a ford. It may be a small weir that is too high to jump, with impounded water that is dangerously warm above it. Or it may be a bridge apron or a culvert with concrete floors so slippy they are impossible to traverse.
She is joined by other migrating salmon. They’re all struggling. She tries to jump over the barrier, but her muscles drain energy, and she tires from repeated attempts. This concrete barrier stymies her ability to reproduce, and eventually, she gives up and floats downstream. Her unique genetics, tied for generations to this river, will die with her exhausted body.
This hopeless scenario is a reality on Irish rivers, because of the tens of thousands of barriers (many obsolete) that congest our waterways and prevent fish from doing what they’ve done for millenniums: freely move up and down the entire length of rivers and streams.
A few years ago, Inland Fisheries scientists identified 73,000 potential barriers to fish migration on Irish rivers – one barrier for every kilometre of river. These blockages to life are among the most significant pressures on waterways. They fragment our rivers and impede the flow of sediments, causing them to accumulate upstream, increasing the risk of flooding. They also weaken a river’s ability to move nutrients downstream; a free-flowing river can help alleviate the immense pressure on our rivers from pollution.
Barriers sometimes pose a threat to humans, too. Weirs can be particularly dangerous. In January 2023, a serious accident involving two boats on the river Corrib’s Salmon Weir nearly cost rowers’ lives. The Marine Casualty Investigation Board concluded that the weir, which has a history of incidents, was a “causal factor” in the accident and warned that a repeat occurrence is likely without remedial action.
But now, a growing band of scientists and river advocates across Europe are removing barriers at a record rate. According to a new report by Dam Removal Europe, last year nearly 500 were taken down across the continent, a 50 per cent increase on 2022, reconnecting 4,300km of water habitat. And it’s happening elsewhere: in the US, 80 dams were removed in 2023, reconnecting 1,865km of river upstream.
Countries such as France, Spain, Sweden and Denmark lead the way as policymakers increasingly realise that barrier removal is a powerful and effective way to restore rivers, reverse nature loss and mitigate the threats from climate change, extreme weather events and flooding.
[ Irish waterways: the toll of years of draining, modification and engineeringOpens in new window ]
Last April, Portugal’s first barrier removal took place. In an initiative spearheaded by Geota, an environmental NGO based in Lisbon, a small weir that stretched 14m across the width of the Alviela river in the centre of Portugal was demolished, immediately restoring 3.3km of river connectivity.
The removal was a milestone for Geota, which has argued that barriers present one of the great global threats to biodiversity and the proper functioning of freshwater ecosystems. Although the Portuguese government did not fund the weir removal, it prompted political change when the minister of environment and climate action announced a new national programme for removing river barriers, of which there are an estimated 30,000. Earlier this month Geota won the European Dam Removal Award in recognition of its efforts.
An alternative to removing a barrier is constructing a fishway, or ladder, to help the fish move up and down the river. But fish passes don’t always work, and they are more expensive to build and maintain than removal. Wherever possible, removal is often cheaper and more effective, especially if the barrier is obsolete.
[ Ecological tragedy in Clare heralds imminent water crisis in IrelandOpens in new window ]
Barriers in rivers act like blocked and clogged arteries in humans; they slowly kill. When they are taken away, life returns in droves and water quality improves. There’s a golden opportunity to help get our rivers back – we should take it.
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