Seeing fish trying to jump a weir isn’t impressive – it’s tragic

On a stretch of road between Aughrim and Tinahely, at the foothills of the Wicklow Mountains, there’s a small three-arched bridge over the Derry Water river. Ballinglen Bridge is a robust structure made of rubble fieldstone that has withstood the passage of humans for two centuries. But for the fish in the waters underneath, this bridge represents one thing: a dead end.

One morning a few weeks ago, I met Luke Drea on the bridge. Luke is a professional horse rider by day; in his downtime he works for the East Wicklow Rivers Trust. As we walked towards the base of Ballinglen, he pointed to the problem: a slippy concrete platform, built to stabilise the bridge, has created a metre-high drop. The water thunders at such a velocity that I could barely hear him speak.

We step back into the field. Luke tells me the barrier at Ballinglen Bridge shuts out Atlantic salmon and trout of 10km of pristine spawning grounds upstream. Their presence in the water is essential for the critically endangered freshwater pearl mussel, also found here, as are our native European eels, river lamprey and brook lamprey.

A free-flowing river naturally meanders with pools and riffles, murmuring as it flows along. Fish use the idiosyncrasies in the water and river bed to dart left and right; they’re equally at ease swimming against the current as they are going with the flow. What fish aren’t evolved to deal with is the rigid, inflexible certainty of concrete and steel.

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But Atlantic salmon, which arrive at Ballinglen Bridge to breed after four years at sea, are heroic athletes whose instinct to reproduce overwhelms any threat of injury. They catapult themselves against the concrete slab to traverse it. If they’re successful, they land on the smooth concrete surface. It’s like an ice rink, and they slip back.

Up and down they go, spurred on by a genetic drive to reach the cool, well-oxygenated waters upstream, but weakened by the effort. Eventually, exhausted, they give up and return downstream to an uncertain fate. (Lamprey exhibit a Mr Bean-like co-ordination when faced with man-made barriers and equally don’t stand a chance.)

What’s happening at Ballinglen is not uncommon. In 2012, scientists from Inland Fisheries Ireland surveyed rivers across Wicklow and found 103 barriers to fish movement. More recently, this work has expanded nationwide to look at Ireland’s 74,000km of rivers and streams. Researchers have identified 73,092 potential barriers.

Culverts are the main culprits – we’re a nation obsessed with them – but dams, ramps, fords, sluices and bridges are also highly problematic. Weirs are hellish for fish. It’s not just that the jump may be too high or the length too long; it’s also that impounded areas upstream form mini-lakes where sediment gathers. These pools act as a heat store, which raises the water temperature. Fish won’t reproduce, feed, migrate or grow if it’s too high.

Seeing fish trying to jump a weir isn’t impressive; it’s tragic.

More than a million barriers have been identified in 36 European countries. But there’s hope. A record 325 were removed last year, the vast majority less than 2 metres high. This has reconnected 832km of habitats. In Denmark, for example, the removal of a 1.1-metre-high weir along the river Idom in Jutland opened up 15km of spawning grounds to adult Atlantic salmon. Within a year, 100 newborn fish just 50 metres upstream emerged.

The move to free Irish rivers needs to gather momentum. If there’s one river to tackle for high impact it’s the Shannon, which is a lethal obstacle course for fish facing injury and death from the hydroelectric dams and weirs. It’s an ecological mess. Public money has been allocated to deal with the obsolete weir at Annacotty on the lower Mulkear river, which IFI scientists say is a complete barrier to juvenile Atlantic salmon and adult lamprey, but progress between State agencies could be faster.

Back at Ballinglen, the East Wicklow Rivers Trust and IFI are looking to nature for inspiration. Because the bridge will likely collapse if the concrete slab is removed, they want to create a “rocky ramp” to taper the steep drop and ease the flow. No concrete, cement or chemicals will be used; instead, 320 tonnes of locally sourced stones will mimic what naturally happens in the river. The hope is that it will reopen up the river’s length to fish.

It’s an enticingly simple prospect, in contrast to the Herculean efforts needed to tackle the impacts of water pollution, rapidly warming oceans and rivers, overfishing and fish farming on our wild fish. But as with so many initiatives in Ireland, the danger is that barrier removal projects get caught up in red tape, endless reports, consultations and slickly produced roadmaps. There really are only so many fish in the sea; time is rapidly running out.

You can help. Go for a walk in your area, look at your local streams and rivers, and download the free Barrier Tracker app developed by European researchers as part of their citizen science “Let It Flow!” initiative, and log any potential barriers you find.

As you do, keep these stats in mind: In 1971, 1.2 million Atlantic salmon returned to Irish rivers to spawn. Last year, 171,000 returned. After they return to their place of birth to breed, they die, so every wild salmon returning to our rivers should be highly valued, like a bar of gold.

Salmon are on course for extinction within our lifetime. We can do nothing, and keep them out. Or we can free as many river barriers as possible and celebrate their final, uninterrupted passage home.