Councils plan to clear paths through weirs on the River Liffey to help revive fish populations

Three Dublin councils are planning to work together to modify at least seven weirs on the River Liffey that block the passage of salmon, trout, eels, and other creatures – so they won’t anymore.

Fingal County Council, Dublin City Council, and South Dublin County Council are looking for engineering and environmental consultants to figure out what needs to be done, and put in planning applications to do it – under a contract that could be worth up to €3 million. 

A survey of 13 major weirs along the middle and lower Liffey found in 2023 that while most had fish passage options designed to allow migrations, they aren’t working well. 

The weirs were built on the river in a different age, when water power was used to run mills. The Islandbridge weir, for example, was used for a variety of purposes, such as production of calico, the survey says. 

“Considered together as a complex, [the weirs] completely block migratory fish species from accessing most of the river and degrade/impound the habitat they need to complete their life cycles,” it found. “Interventions are now required to improve the Liffey’s fish community.”

Mark McAndrew, director of the Liffey Salmon Project, had just wrapped up fishing and was packing up his rods when he answered the phone on Friday, 13 June.

He’s been advocating for years for actions that would help salmon populations on the Liffey to rebound, and he says what the councils are planning would help. He’s seen such interventions work elsewhere. 

Built heritage vs biological heritage

The population of salmon in the Liffey has dropped drastically for a number of reasons, says Brian Coghlan, a research officer at Inland Fisheries Ireland, which administers the grant schemes focused on modifying or removing barriers to fish on waterways.  

Water quality, and obstructions like weirs and dams are among them, Coghlan says. 

“They all get stuck below the weir, and they have to spawn there, instead of migrating maybe 50 or 60 kilometers upstream,” he says. “And that will have an effect on the population.” 

Meanwhile, the river has been fundamentally transformed, Coghlan says. Now, 60 percent of it is basically a lake rather than a river, because there’s no flow – and salmon need flowing water, as well as the right kind of gravel terrain, to flourish, he says.

One of the challenges of such projects is that it is sometimes unclear who owns them, which can create legal difficulties, says McAndrew. Another is that local residents object to the removal of weirs.

"We've got this conflict between our built heritage and our natural heritage in terms of migratory fish species,” Coghlan says.

People who want to preserve the weirs because they are part of Dublin’s built heritage need to be heard out, Coghlan says. But he also said he thinks “biological heritage” should be prioritised – that is, unblocking fish paths.

Removing barriers on rivers is not only effective at increasing fish populations, but also has economic benefits, says Craig Bullock, a research fellow at UCD’s School of Architecture, Planning and Environmental Policy.

“There's a lot of benefits,” Bullock says. “To migratory fish anyway, which is mainly, mainly salmon, but also trout to some extent.”

“So these salmon and trout, they make quite a serious economic contribution in terms of visiting anglers and national anglers who have to buy licences and permits,” he said. “So there's a tourism dimension to it as well.”

The tender that's out now is to hire consultants to make a proposal and apply for planning permission to unblock the river to help revive the fish population. It will take years before any work on the river actually begins, says Coghlan.

“Things take time, like with anything in government,” he said.

Funded by the Local Democracy Reporting Scheme.