Festival-goers have gathered in North Ronaldsay in Orkney to help build a 13 mile (21km) stone dyke.
The annual event draws volunteers from around the world and includes dyke building, workshops, music and a ceilidh.
The wall is required so that the unique seaweed-eating sheep are prevented from venturing onto the grass.
An enzyme in seaweed stops the ancient breed of sheep being able to process grass and which can lead to copper poisoning.