Gardaí say the four men and three women were detained for alleged public order offences when they entered the sea in an area where contractors were carrying out preliminary work on the gas pipeline.
Five of those arrested were UK citizens; two were Irish.
The protestors who put to sea in kayaks are opposing the controversial pipeline on health and safety and environmental grounds.
The world's largest offshore pipe-laying ship, the 'Solitaire', is due to begin work in the area when weather conditions permit. It is currently docked in Killybegs.
