We present a comprehensive regional bathymetric data compilation for the southwest Indian Ocean (swIOBC) covering the area from 4°S to 40°S and 20°E to 45°E with a spatial resolution of 250 m. For this, we used multibeam and singlebeam data as well as data from global bathymetric data compilations. We generated the swIOBC using an iterative approach of manual data cleaning and gridding, accounting for different data qualities and seamless integration of all different kinds of data. In comparison to existing bathymetric charts of this region, the new swIOBC benefits from nearly four times as many data-constrained grid cells and a higher resolution, and thus reveals formerly unseen seabed features. In the central Mozambique Basin a surprising variety of landscapes were discovered. They document a deep reaching influence of the Mozambique Current eddies. Details of the N-S trending Zambezi Channel could be imaged in the central Mozambique Basin. Maps are crucial not only for orientation but also to set scientific processes and local information in a spatial context. For most parts of the ocean seafloor, maps are derived from satellite data with only kilometer resolution. Acoustic depth measurements from ships provide more detailed seafloor information in tens to hundreds of meters resolution. For the southwest Indian Ocean, all available depth soundings from a variety of sources and institutes are combined in one coherent map. Thus, in areas where depth soundings exist, this map shows the seafloor in so-far unknown detail. This detailed map forms the base for subsequent studies of e.g. the direction of ocean currents, geological and biological processes in the southwest Indian Ocean.