Irish Rail was warned about visible seabed erosion in the Malahide viaduct five days before its collapse.
A leader from the Malahide Sea Scouts spoke to an engineer from the rail company to warn of potential danger to the Belfast-Dublin line after they noticed what appeared to be seabed erosion and a change in water flow in the estuary. Following his phone call, an inspection was carried out three days prior to the collapse of one of Ireland's busiest lines.
However, the area was given the all clear and rail travel was allowed to continue.
Ivan Barrett, a canoeing leader with the Malahide Sea Scouts said he noticed the erosion increasing over the past two to three months and became particularly concerned two weeks ago.
Mr Barrett said: “For a number of weeks, fluid had been increasing around the fourth and fifth arches of the estuary. It was on the 14th that I noticed rocks had fallen beneath the pillar.”
He then called Iarnrod Eireann and spoke to an engineer to “walk him through” his observations.
He said: ”I am not qualified to comment on structural things, but I had seen enough erosion over time to make me concerned. From a canoeing perspective, I noticed the flow of water changing and started to get concerned.”
Seabed erosion is suspected of being behind the collapse.
A spokesperson for Iarnrod Eireann said: “We received several calls from the public on Monday 17 about erosion marking on piers of the viaduct. However, the calls did not suggest a collapse would be a danger, but expressed concern to what they had seen, to which we responded promptly with an inspection.
“Any visible evidence from that inspection was cosmetic, not structural damage.”
The collapse of the bridge has caused chaos among commuters and now Iarnrod Eireann is offering commuters who have purchased monthly or annual passes, who have decided against using the bus service, a full refund.
Repairs are expected to take a minimum of three months.