Maartensgat is a marina tucked beneath the Grote Kerk in the historic heart of Dordrecht, situated on the Oude Maas.

The harbour is reached by crossing a manually operated cast-iron swing bridge from 1868, the Mazelaarsbrug, which serves as the VHF channel 74 call sign for reaching the harbourmaster.

The setting places visiting boaters directly among Dordrecht's monuments, shops, and restaurants. The marina is open to visitors and welcomes transient boaters, though reservations are not accepted.

Visitors are advised to contact the harbourmaster before entering, as an alternative berth at the neighbouring kdr&zv de Nieuwe Haven may be suggested if space is limited.