'Rock ramp' used in Wicklow river to solve blockage issue

Researchers have established that Ireland has 74,000km of rivers and streams but 72,000 blockages along those waterways.

These are man-made structures including culverts, weirs, dams, ramps, sluices, and concrete supports for certain bridges. These blockages represent huge challenges for migratory fish.

In many cases salmon, trout, eel, and lamprey, simply cannot swim past them to get up-river to spawning grounds or complete their life cycle.

That figure - 72,000 blockages over 74,000km – is an astounding interference to the ecology of what should be free-flowing rivers in Ireland.

However, the EU Nature Restoration Law, passed earlier this year means we are now legally obligated to deal with many of those blockages where they are causing ecological harm.

The aim is to restore biodiversity and secure the things that nature does for free.

At a place called Ballinglen, not far from Tinahely in south Co Wicklow, an old fieldstone bridge has arched over the River Derry for more than two-hundred years.

Architecturally it is a beauty, with three stone arches above the water. Below water however, it is a dead end for migratory fish species.

It has been that way since some time in the 1960's when a big 1.4m concrete plinth was added to strengthen the foundations of the bridge so it could survive big flood events.

The fish simply cannot jump that plinth. It is far too big.

The result is that there have been very few salmon, trout, eel, or lamprey in the 10km of pristine waters upstream from the bridge for the past 50 years.

All that is now about to change however, thanks to a big local effort led by the East Wicklow Rivers Trust.

The trust is a voluntary group of ecologists, river enthusiasts, fisheries specialists and politicians who came together in 2019 to provide a voice for rivers and promote awareness about the ecological issues affecting them.

Thanks to their efforts an expert ecological engineering company called Rivus has just spent the past two weeks building the most natural looking rock-ramp fish pass to enable even the smallest fish overcome the big concrete barrier than has kept them at bay for more than half a century.

The work involved the creation of a series of gently ascending water pools by using natural stones to make a series of dams each about 7m apart.

These ascending pools mean the fish will no longer have to jump the big concrete plinth to get upstream.

From now on they just need to do a series of smaller far easier jumps through the gently rising sequence of pools to get past the bridge.

The East Wicklow Rivers Trust employed Rivus Ecologist Alan Sullivan to take charge of the project and its construction.

He said it is vital to start looking at barriers to migration in rivers all around the country so that salmon, whose numbers are in freefall, can reach the best areas to breed in, and have their offspring.

"This structure we have built is designed in such a way that even the smallest fish can move through it. It is a style of fish passage that we call nature mimicking, or ecological engineering, and it is an approach that has been gathering pace in America and Europe.

"We decided to mimic how a river naturally functions. We don't use any concrete; we don't use any man-made materials. Everything, even stone sizing, is based on what we would find naturally occurring in river systems. That allows it to become a living structure itself. All those riffles and pools and glides that we have now built will operate like a reef. It's like a little coral reef within a river.

"There are so many places for different creatures that live within the river to hide in, or to live within that structure itself. It doesn't need to be clean or maintained because of the way it is designed.

"Trees will roll off it, trash rolls off it, and the speed of the water and the aggression of the water will stop it from silting up as well."

Sometimes described by ecologists as the arteries of our planet, rivers are amongst the most degraded environments on earth.

They are under constant threat from pollution, urbanisation, industrial development, climate change, excessive extraction of water, and habitat loss.

Over the past decade 71% of fish and 60% of amphibian populations throughout the EU have suffered a decline. Ireland is little different.

Inland Fisheries Ireland records show almost 19,000 fish died in 30 recorded fish kill occurrences in Irish rivers between January 2023 and July 2024.

Those mortalities included Atlantic salmon, trout, eel and lamprey of all ages. In all cases the ripple effect of the ecological damage associated with such fish kills is long lasting.

Historically, impacts from agriculture have been the number one cause of fish kills in Ireland. Of course, there are many other causes too.

Eutrophication, or a lack of oxygen in fresh water due to the growth of algae, has also decimated local fish populations.

So too have impacts from industry, municipal activities, mining, construction and other causes. In some case none of those factors are involved in fish killings.

For instance, between June and July this year 1,079 salmon were found dead in Ballisodare River in Co Sligo. That was 12.8% of the total salmon stock in the river.

Inland Fisheries Ireland said the fish died because they had arrived in the river exhausted and stressed from a challenging sea journey into very low water conditions in the Ballisodare river.

Because the water was low, they were forced to congregate and that facilitated the outbreak of disease.

Ecologist and founding member of the East Wicklow Rivers Trust, Faith Williams, said this is the United Nations decade for ecological restoration.

She said we have a biodiversity and climate crisis. We need functioning rivers, and we need them to achieve good or high status under the EU Water Framework Directive.

"There are a lot of challenges to fish migration. It could be something as simple as a farmer putting in a culvert and not properly setting it into the bed of a river.

"We have a Nature Restoration Law coming into play. The kind of project that we have just completed at Ballinglen bridge in Co Wicklow is the kind of thing they are trying to address.

"Hopefully by us removing the barrier that was making the river fail we have sorted out the hydro morphological challenge of the river.

"Now we should have the river in really good condition provided all the landowners upstream continue to manage and farm their lands in a way that does not lead to pollution in the river.

Ecologist and Social Democrat TD Jeniffer Whitmore is another founding member of the trust. She said work at Ballinglen bridge has been a long time in the making.

"We've been working on this project now for a number of years. We had to make sure that was done properly, that by putting something like this into the river it was not going to damage the environment or the river system. A lot of thought was put into it. The best science was used to design a system that is most suitable for the fish and for this specific river.

"This is something we probably will be seeing much more of. It is the best thing we could do for fish in our river systems. Get rid of those weirs and those dams and those obstructions. It is probably the most practical element of the Nature Restoration Laws and projects that we could do. It would deliver the biggest bang for buck for our fish populations and it's great to be involved in one of the first of these projects in the country."

Alongside the East Wicklow Rivers Trust and the Rivus ecological engineering the other partners who contributed to the success of the Ballinglen Bridge project included Inland Fisheries Ireland, Lawpro, Wicklow County Council, the National Parks and Wildlife Service, and the local landowners.