Deutsches Sielhafenmuseum in Carolinensiel, Maritime heritage museum in Carolinensiel, Germany.

Deutsches Sielhafenmuseum in Carolinensiel is a harbor museum in northwestern Germany spread across several historical buildings and featuring a basin with traditional sailing boats. The collection documents coastal North Sea life through authentic harbor structures and vessels that show how people worked here and the role the harbor played.

In 1978 Gert Schlechtriem, director of the Deutsches Schifffahrtsmuseum in Bremerhaven, proposed a museum for the Sielhäfen; the Förderkreis was founded and Frerich Eilts acquired exhibits. The museum opened on 8 June 1984 in the Groot Hus, a former grain store of 1840. The Alte Pastorei (1994), Kapitänshaus (1997) and Rettungsschuppen (2005) followed, and the harbour basin was restored in 1986–87.

The museum's name refers to the Sielhäfen, tidal sluice harbours of the Wadden Sea coast, where a distinct harbour culture developed in the 19th century. The Kapitänshaus of 1803 presents the daily life of seafaring families, while the Groot Hus of 1840, a former grain store, traces the shift from trading harbour to museum harbour. Since 1990 the harbour has again been entered by traditional sailing ships, which gather each August for WattenSail.

The museum opens most days and can be explored through three main buildings, each showing different aspects through its collections. Plan to spend enough time visiting all areas and viewing the vessels in the outdoor basin.

The museum cutter "Gebrüder AZ 5", launched in 1929, was restored in 2001 and is seaworthy again; it lies in the museum harbor in front of the Alte Pastorei and makes trips in the Wadden Sea. The four exhibition buildings are joined by the Museumsweg Carolinensiel, with 19 theme boards and 18 site boards on land reclamation and the history of Carolinensiel and Harlesiel.