Schlüttsiel, Harbor terminal in Nordfriesland district, Germany.

Schlüttsiel is a ferry harbour at the end of the Hauke-Haien-Koog dyke in the municipality of Ockholm, about 2.5 km east of Hallig Oland. It consists of a harbour built in 1959 with a handling terminal and a vehicle loading station, plus a historic sluice building. The sluice has four gates, each 6.5 m wide, draining the Bongsiel Canal into the North Sea.

The current terminal opened in 1959, replacing the older harbor at Bongsiel, which had previously served island transport. The move was driven by the need for deeper water access and a more reliable approach for larger vessels.

The name combines the North Frisian word slüütj, meaning a marsh ditch, with Sil, a sluice in the dike. The first element refers to the Slut tidal current that begins here, passes Gröde and Oland and flows into the Sønderaa. Ferries run to the halligs Langeneß, Gröde and Hooge and, in summer, to Amrum.

In summer, traffic at the terminal rises sharply, so arriving early is a good idea, especially if you plan to bring a vehicle. The site has waiting areas, restrooms, and a small food counter near the quay.

The sluice at Schlüttsiel, built in 1959, has four gates each 6.5 metres wide, discharging water from the Bongsiel Canal into the North Sea. The name combines North Frisian "Slüt", a tidal channel, with "Siel", a dyke sluice; the channel begins here, passes Gröde and Oland and reaches the Sønderaa. The old harbour was at Bongsiel, founded in 1735.