From Wikipedia:
The Norderbootfahrt is a canal on the Eiderstedt peninsula. The canal built in 1612 led from Tönning at the mouth of the Eider to Tetenbüll. Garding and Katingsiel could be reached via a connecting canal (built in 1615) to the Süderbootfahrt. The Norder and the Süderbootfahrt connected the Eiderstedt hinterland by water with the open North Sea and thus primarily ensured the rise of Tönninger Hafen to become the most important port in the region.[1]
It was created shortly after the construction of the southern boat trip from Garding to Katingsiel. Finally, in 1615, both canals were connected. Katingsiel then lost its position as a port to Tönning. The canals could hold ships of 8 to 10 tons, and the narrow canals were used for towing. The port of Garding, which has now been filled in again, was also created as part of these construction measures.
The construction had become necessary because Eiderstedt's agriculture was booming at the time. Before the religious wars and persecution in their own country, the Dutch had reached Eiderstedt via the southern North Sea. There they brought agricultural innovations with them, especially in milk and cheese processing. At the same time, numerous natural waterways on Eiderstedt had fallen victim to increasing diking and land reclamation. The canal was also made possible by the Dutch and their knowledge of hydraulic engineering: the concept for the Norderbootfahrt came from Caspar Hoyer and the Dutch who had immigrated to it.