Beltringharder Koog, Nature reserve in Nordfriesland district, Germany.

Beltringharder Koog is a protected nature reserve in Nordfriesland with lakes, wetlands, and meadows spread across its terrain. These varied habitats support numerous bird species that occupy the area according to the seasons.

The area was created in 1987 through a land reclamation project that transformed a section of the Wadden Sea into a protected zone. This transformation connected the former island of Nordstrand to the mainland.

The name recalls the Beltringharde, a district destroyed in the Burchardi flood of 1634; the new koog lies south of that lost territory. At the Arlåen outlet a nature centre offers guided excursions into the reserve, and the dyke's two sluices, Lüttmoor Siel and Holm Siel, let visitors watch water flow between the Wadden Sea and the enclosed basin.

Four observation huts are positioned around the reserve and offer good views of waterfowl and wading birds. Since these huts remain accessible year-round, visitors can observe birds during any season.

The dyke's base is 100 metres wide and carries two sluices, Lüttmoor Siel and Holm Siel, where the Arlåen stream reaches the North Sea. Plans for a much larger enclosure of about 5,600 hectares were cut back to roughly 3,400 hectares after protests by environmental activists.