what is an island? an island is a piace of land completely surrounded by water, but a Hallig is a special type of island in the North Sea. There are nine island of the Frisian coast of Germany and hundreds of years ago they were separted from the mainland by flooding and erosion. The Hallig island consist of SALT MARSHES. There are lots of hills with houses and a few protective trees on top. They are mini island is a magical marine world.