The Department of the Marine and Natural Resources says it has identified the source of a mystery "slick" which appeared in Broadhaven Bay, Co Mayo, last month.
The pollution has been traced to waste mushroom compost, which may have been dumped illegally, according to the Department. Reports of the brown slick were received by it on September 5th, and initial descriptions had suggested that it might have been a form of algal bloom or red tide.
Samples of water and sediment were sent to the Marine Institute's phytoplankton laboratory but there was no indicator of an algal bloom. The Department says that "information was subsequently received" to the effect that waste compost might have been responsible.
This information was investigated, and the Department said it was now satisfied that illegally dumped waste mushroom compost was the source. Inquiries were continuing into the illegal dumping, it said.
The Erris Inshore Fishermen's Association had suggested that the slick could be linked to seismic tests being undertaken offshore by Enterprise Energy Ireland (EEI), as part of the Corrib gas field project. A dead whale had also been washed up and the association called for a post-mortem on the cetacean.
However EEI vehemently denied that it was the source of the pollution. It confirmed that dyes had been used to examine currents as part of environmental impact assessment work.