The fish were discovered at Downings beach on Saturday morning and the cause, so far, is a mystery.
A holidaymaker told BBC News NI she was shocked to find the fish during a morning walk.
"The lifeguard said he thought the high tide had washed them onto the beach, but no one has ever seen anything like it before," Amanda Meehan said.
Various possible causes have been suggested to BBC News NI including the tide and rough weather.
Hundreds, if not thousands, of dead fish have been found after a stormy night on Downings beach in County Donegal. Video sent in by Amanda Meehan. #Donegal pic.twitter.com/pZtQlcvgTS
— Barra Best (@barrabest) August 31, 2019













Comment: Radio Dabanga reports on September 1: