There was been oil on the River Eske in Donegal Town throughout the day.
Residents are gravely concerned about the oil which they say almost entirely covered the river by late morning on Thursday.
The oil could clearly be seen entering the Eske from a brook in the Drumlonagher area.
Due to persistent rainfall, the Eske was in full and fast flow all day Thursday. The oil was being carried out through the estuary and into Donegal Bay.
Dismayed residents are also reporting an unpleasant oily smell from the river and Bay.
The River Eske is home to a diverse range of wildlife along its course and in the tidal estuary, as well as being a prominent feature of the town.
Residents are calling for an investigation into the matter, as well as assurances that it will not happen again.
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