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"It was terribly traumatic to look at the families watching out over the lough and praying," he said.

Northern Ireland Water has admitted breaching the law hundreds of times each year by releasing untreated sewage into the lough.

Several crews simply failed to return, while others are thought to still lie below the surface of the lough.

It did leave the port just after 23:30, but remained in the lough for almost three more days before departing at about 16:30 on Thursday.

The lough supplies half of Belfast's drinking water and 40% of Northern Ireland's overall.