Up to 50 boats took part in a demonstration rally on the River Shannon to highlight opposition to Uisce Éireann's plans to extract water from the river to serve the greater Dublin region.
Uisce Éireann has applied for planning permission for the project, which is the largest water project in Irish history.
It proposes constructing a 170km steel pipeline that will pump drinking water from the River Shannon, at the Parteen Basin below Lough Derg, to the Midlands, Eastern and Greater Dublin area.
The water utility proposes to abstract a maximum of 2% of the average river flow.
The estimated cost of the project is €4.6 billion.
The rally was organised by angling groups from the Shannon region.
Speaking at the protest, one of the organisers, Cristopher O’Meara, said the billions of euro being proposed for the project would be better spent on supporting development in the west.
"We are told that this project is crucial for future development purposes in the Eastern Region, but what about the west," he said
"We think this plan will have a negative impact on the River Shannon, on its ecology and on those that fish and earn a living from the river and it should not go ahead," he said.
Watch: Up to 50 boats rally over Shannon to Dublin pipeline plan
The rally was also attended by Tipperary Fine Gael County Councillor Phyll Bugler.
She said "the message I want to send to Uisce Éireann is - like Greenland, Lough Derg is not for sale. I would ask them to look at other alternatives in the eastern region for a more suitable solution to Dublin’s water shortage issues".
The rally was also attended by Tipperary Labour Party TD Alan Kelly.
He said there are huge concerns in the region about the potential impacts of the project on the Shannon.
"But I would also have questions as to whether Uisce Éireann can actually deliver this project. I would also have concerns regarding the cost of the project and whether this is value for money," he added.
Uisce Éireann said the proposed pipeline is "a critical infrastructure project", which would provide a "resilient, safe, and secure water supply with capacity to address the water supply needs for up to 50% of the population".
The company said water levels would remain "unchanged and undiminished under this proposal" and that there would be a "neutral effect" on water quality.
It said the project is also "critical to the delivery of housing and growth" nationally and its planning application will "secure a new source of water from the River Shannon at Parteen Basin, abstracting a maximum of 2% of the long term annual average flow of the River Shannon at Parteen Basin".
Uisce Éireann said it had submitted environmental impact assessment reports as part of its planning application.
"We need a new sustainable source of water alongside continued leakage reduction. Fixing leaks is essential, but it’s only part of the solution," it said.
If planning permission is granted, Uisce Éireann proposes to start construction in 2028 and complete it within five years.
