Picture, if you will, a wild salmon navigating the expansive ocean waters. Having spent two years in the Scandinavian Sea, she has grown in size, vitality, and her capacity to breed through consumption of capelin, shrimp and sand eel. She has evaded fisherman’s vessels and eluded devastation by bacterial illnesses and parasites such as sea lice.
Early spring finds her overwhelmed by the hereditary urge to return and spawn in the river where she originated. She undertakes a journey of 2,000km towards Ireland’s coastal fringe and makes her way to the start of her birth estuary. The surfeit of nutrients has induced extensive algae growth which has depleted the oxygen in the water, nevertheless, she succeeds in advancing into the freshwater of her inception river, outmanoeuvring predators like otters en route.
The river’s water temperature is marginally warmer due to global warming, inducing stress in the salmon when it exceeds 20 degrees. Undeterred, she fights against the flow to reach the source, where she requires chilly, unpolluted water abundant in oxygen and ample clean pebbles to dig a nest and spawn.
However, on the brink of accomplishing this tremendous, treacherous voyage, she is confronted with a bitter obstacle; a concrete wall. This hindrance may take the form of a hydroelectric dam, a ford or a sluice. It could be a minor weir too elevated to leap over, with trapped water that is dangerously hot above it. Otherwise, it could be a bridge apron or a conduit with concrete flooring too slick to cross.
Joining her are fellow migrating salmon, all of them in distress. Endeavouring to leap past the blockade, her muscles sap of energy from the repeated efforts. Her capacity to breed is thwarted by this concrete obstacle, forcing her to eventually surrender to the current and float downstream. Her unique genes, tethered to this river for countless generations, will perish with her weary body.
Such dispiriting circumstances ring true in Irish waterways owing to the myriad of barriers (numerous of which are redundant) that obstruct our rivers and prevent fish from their natural millennia-old habit of moving unimpeded along the entire length of rivers and streams.
Several years back, scientists from Inland Fisheries identified approximately 73,000 obstructions impeding fish migration in Irish rivers. This equates to one impediment for every kilometre of river. These significant deterrents, obstructing river flow and sediment movement, increase flood risk as sediments build up upstream. Additionally, these deterrents undermine the river’s capacity to transport nutrients downstream. Besides, these hindrances can also pose a human threat, with weirs being notably hazardous. An unfortunate accident happened at the Corrib river’s Salmon Weir in January 2023, nearly resulting in the loss of rowers’ lives. The Marine Casualty Investigation Board determined the weir was a causal agent and warned of potential further accidents unless remedial steps are taken.
Recently, however, there has been a surge in the number of scientists and river advocates across Europe focused on removing these barriers at an unprecedented rate. A fresh report from Dam Removal Europe reveals that nearly 500 barriers were removed last year across the continent, marking a 50% increase from 2022, and reconnecting 4300km of water habitats. Similar progress is being observed in the US, with 80 dams removed in 2023, re-establishing 1865km of river upstream.
Countries such as France, Spain, Sweden, and Denmark are pioneering this initiative as policymakers increasingly acknowledge the power of barrier elimination in river restoration, reversing nature decay and reducing climate change, extreme weather and flood risks.
In April of the previous year, Portugal marked its first barrier removal. Led by Lisbon-based environmental NGO Geota, a small weir extending 14m across the Alviela river’s width, centrally located in Portugal, was destroyed, instantaneously restoring 3.3km of river connectivity.
The eradication represented a significant achievement for Geota, who have maintained that obstructions pose one of the most severe global dangers to biodiversity and the smooth operation of freshwater ecosystems. The Portuguese government did not directly finance the weir removal, yet it instigated political reforms when the minister of environment and climate action advocated for a novel nationwide programme for the elimination of river obstructions, which are generally believed to be around 30,000. Notably, Geota received the European Dam Removal Award for their remarkable efforts earlier in the month.
Instead of eradicating a barrier, a fish pass, or staircase, can be established to enable the movement of fish along the river. Nevertheless, these fish passes are often ineffective and pricier, both in construction and maintenance than discontinuation. Hence, in most cases, removal is frequently less expensive and more efficient, particularly when the barrier is out of date.
Comparable to blocked arteries that slowly lead to the demise in humans, river barriers share a similar fate. Their removal rejuvenates life and enhances water quality. We certainly have a unique chance to revive our rivers, and it behoves us to seize it.