Karsibór (German: Kaseburg) is an island in the Oder Lagoon, Poland, which was created artificially by a channel cutting it off from the island of Usedom. The island was named after its largest village (now part of the town of Świnoujście).
In 1880, the Kaiserfahrt (Emperors's passage) channel on Usedom was opened, a water route with a depth of 10 metres connecting the lagoon with the Baltic Sea by bypassing the eastern part of the Swina arm of the Oder River, allowing large ships to enter the lagoon and the seaport of Stettin (Szczecin) quicker and safer than on the natural river bed (Alte Swine) which separates the river from the island of Wolin in the north.
The canal, approximately 12 km long and 10 metres deep, was dug by the German Empire between 1874 and 1880, during the reign of the first Kaiser Wilhelm (1797 - 1888) after whom it was named.
After 1945, not only areas east of Oder Neisse line became part of Poland, but also control of the former German seaport cities of Stettin (Szczecin) and Swinemünde (Świnoujście) on the western bank of the river Oder was granted to Poland which renamed the canal after the Piast dynasty.
Also affected was the village of Kaseburg. It was named Karsibór, has now ca. 1,000 inhabitants and is part of the commune of Świnoujście (Swinemünde) which is also on Usedom.