In Swords, a cascade at Usher’s Lake is preventing the migration of fish up the Ward River, according to a new ecological study.
The waterfall is one of five barriers – among them weirs and rock armour – along a 6km stretch of the river, according to Alan Sullivan, director of Rivus, an ecological engineering consultancy.
About 80km of river sits upstream of the cascade, Sullivan told councillors at the Balbriggan/Rush-Lusk/Swords Area Committee meeting last Thursday.
“So the actual lungs and heart of the river is being prevented from being utilised by a range of endangered species that we need to get into these areas,” he said.
These barriers impact the ability of fish to spawn, and can make their population more vulnerable to predators, Sullivan said, after the meeting.
And the loss of any species can damage a river’s ecology, he says. “When a river is functioning properly – because everything is connected – everything aids everything else, and if one or two species go missing, it has a knock-on effect on every other species.”
The Rivus survey looked at how to reconnect the ecology along the Ward River, so it can flow uninterrupted all the way along into its downstream reaches and water courses, said Sullivan.
Sullivan said, at the meeting, that the council and the Office of Public Works would be turning to what are known as “nature-based solutions” – the use of natural features to sustainably manage an environment – creating wetlands, removing weirs and replacing rock armour with vegetation to protect river banks.
The survey – which looked at a portion of the meandering Ward River between Knocksedan and Balheary Park – is the first step in Fingal County Council’s wildlife enhancement scheme for the river. A council spokesperson said that work on the scheme should start next summer.
It ties in with the redevelopment of the Ward River Valley Park and the council’s Biodiversity Action Plan, the spokesperson said.
At the moment, salmon have disappeared from the river.
It was disappointing not to find any lamprey or Atlantic salmon in this stretch of the Ward River, unlike in the Dodder, said Sullivan at the 9 November area meeting.
“The rivers are quite close to one another and the Dodder is getting very good runs of salmon,” he said.
Green Party Councillor Ian Carey said the lack of salmon was especially sad to hear. “Because it’s described as a salmonid river.”
Sullivan, of Rivus, said the survey did find eels. “But what we saw from the data was that the eels and actually all fish species are not being able to progress up above the cascades.”
The cascade prevents their ability to spawn, Sullivan said, speaking on Tuesday afternoon. “They can’t get into the areas that they need to.”
A barrier like this can trap large numbers of salmon and eels, which makes them vulnerable to predators, he says. “They turn into a smorgasbord for herons. The exploitation rate for juvenile salmon and eels goes up exponentially.”
If the waters around the area of a weir or cascade become polluted, it can also lead to high death rates among fish, he says.
Sullivan pointed to problematic hard infrastructure, such as a concrete weir – a small dam – in Balheary Park, preventing the movement of lamprey and eels.
There are two weirs in the park, and the Office of Public Works (OPW) has asked that they be removed, according to a council spokesperson.
It is unclear what the weirs are for, Sullivan said at the meeting. “None of us have been able to ascertain what the function of those weirs was. Not even the OPW.”
But it is clear that they are barriers, he said. “These are relics of the past that we wish to remove and replace with rubble or cobble mattresses that will increase diversity for potentially crayfish, for other species.”
The council plans to do flood modelling before it takes out the weirs at Balheary, a council spokesperson said.
Rock armour put in to supposedly protect the banks of the river between Usher’s Lake and Balheary Park is also damaging the ecology of the river, said Sullivan at the meeting.
“It actually eats the bank upstream and downstream, and it provides little to no cover,” he said.
The rocks are undermined because they don’t absorb the energy of the river, he said. “The potential for them to completely collapse in an instant is actually quite high.”
Rock armour, used a lot along the river through Swords, should be swapped for a more natural means of riverbank protection, he said. “We can just soft engineer it, or let the banks develop themselves.”
Carey, the Green Party councillor, asked if creating natural banks might cause the river to move. “It could be problematic in the weir down in Balheary Park, because it’s actually pinned between playing pitches and a business park.”
Removing the rock armour will not affect the footpaths, but it does offer an opportunity to move these walkways back a couple of metres, Sullivan said. “And, you know, give some privacy to the river.”
More vegetation is important, he said. “Vegetation is the natural netting that brings our riverbanks together. When we remove that vegetation, or we constantly cull it, we weaken our banks, and leave them prone to erosion.”
The survey found high rates of human disturbance to local species, said Sullivan. “We witnessed directly discharge coming in from land drainage, storm pipes.”
Surveyors couldn’t find kingfishers, dippers or otters in the Ward River Valley Park, he said. “A lot of this has to do with how we’ve assessed the pressure of constant contact from walkers immediately on the riverbank and dogs.”
They spotted evidence of their habitats within the town, but in areas where people couldn’t see in, he said. “So there’s a very strong correlation between otters, kingfishers, dippers and disturbance.”
Any signs of otters in the river is still great news, Carey said, on Monday after the meeting. “I’ve been worried we had lost them because of the human disturbance, because I didn’t know anybody who had seen them there in years.”
It is also remarkable that they are able to be so far upstream, he said. “Even without high numbers of fish on the river because of the impact of the weirs.”
Given the concern around a lack of salmon, Fianna Fáil Councillor Brigid Manton asked at the meeting if the river would be restocked and whether any of this would impact a local tradition of angling.
“I’m just wondering to what extent are we going to have fishing along the river?” she asked. “And is the child with the bucket and the little fishing net going to be banned now?”
Sullivan said he wasn’t in favour of restocking under any circumstances, for genetic reasons. Nor did he support bringing domesticated fish into a wild environment, he said.
“There may be down the line some options for very specific Atlantic salmon egg baskets that might kickstart the river,” Sullivan said.
But fishing wouldn’t become a thing of the past, he said. “The river’s for everybody.”