Þerneyjarsund is a large channel of water between the islands Þerney and Gunnuey.
Þerney island is found in Kollafjörður and is named after the Arctic tern. During the summer months, the island is used as a haven for farm animals. The island is also home to the ruins of a 13th Century church.
Þerneyjarsund makes up just part of a local nature reserve, alongside the islands of Lundey, Akurey and Engey.