Sea angling brothers John and Pat Cunningham described the "beautiful sight" of two orcas who emerged from the water by their rowing boat half a mile from the coast off Glencolmcille.
"I've only ever seen them in the North Sea when I was commercial fishing up there", said John of the unexpected rendezvous.
The Irish Whale and Dolphin Group's record of the sighting speculates that the killer whales may be the same pair spotted off Mizen Head in Cork on 11 June and Slea Head in Kerry a day later.
Killer whales are a rare sight so close to the shore but they are no strangers to Donegal - as last year's appearance of a well known orca pod in Lough Swilly demonstrates.
However, fears were expressed earlier this year that that particular family, often seen off the coasts of Scotland and Ireland, is on the 'brink of extinction'.