An 800m section of Shell pipeline from the Corrib gas processing plant has come loose and is floating under the sea.
Both Shell Ireland and Environmental Protection Agency (EPA) are investigating the incident off the north Mayo coast.
A Shell spokesperson said the pipeline was a piece of plastic ducting measuring 800m in length and carried treated surface water collected at the Bellanaboy terminal to around ten miles out to sea.
The ducting had been secured under heavy boulders and investigations will examine if bad weather in recent days contributed to it coming loose.
Marine vessels have been dispatched by Shell to investigate the matter.
“There is no evidence the pipeline snapped or has broken off, but it has risen to the sea bed,” a Shell spokesman said.
He said the pipe was installed in 2009.
The first gas from the Corrib field will be pumped from the middle of this year.
A company behind the controversial Corrib gas project - Canadian firm Vermilion Energy - used complicated corporate structures in Luxembourg to cut its tax liability as it spent tens of millions of euro to help bankroll development of the gas field, leaked documents show.