The Frisian Islands stretch from the northwest of the Netherlands through Germany to the west of Denmark. Although they are considered a single physical feature, they are divided into West, East and North Frisian Islands – with the North Frisian Islands visible here.

The North Frisian Islands are split between Germany and Denmark. There are four larger islands that make up the archipelago: Sylt, Föhr, Amrum, and Pellworm.

Sylt, the largest of the archipelago, is around 100 sq km and is known for its distinctive shape of its shoreline. Sylt extends in length more than 35 km and, in some places, is only 1 km wide. A sandy beach stretches across the islands’ west coast, however it has begun to erode owing to storm tides. The northernmost island of Germany, it is connected to the mainland by the Hindenburgdamm, an 11 km-long causeway.

The Wadden Sea on the islands’ east side, between Sylt and the mainland, is part of the Schleswig-Holstein Wadden Sea National Park and has been a nature reserve and bird sanctuary since 1935.

The islands of Föhr and Amrum are visible southeast of Sylt. The larger Föhr is called the ‘Green Island’ due to it being sheltered from the storms of the North Sea by its neighbouring islands. The island of Amrum features an extended beach area along its west coast, which faces the open North Sea. The east coast borders to mud flats and tidal creeks of the Wadden Sea.

The three white islands visible below Amrum are the North Frisian Barrier Islands. These sand banks, or shoals, act as a natural breakwater for the smaller islands closer to land. Just east of these lies the island of Pellworm.

North of Sylt lies the Danish islands of Rømø, Mandø, and, lastly, Fanø. In the top-left of the image, a large algal bloom is visible in emerald green. Harmful algal blooms caused by excessive growth of marine algae have occurred in the North Sea in recent years, with satellite data being used to track their growth and spread. These data can then be used to help develop alert systems to mitigate against damaging impacts for tourism and fishing industries.

This image is also featured on the Earth from Space video programme.