OpenSeaMap is an extension of OpenStreetMap that provides a full map of the seas and oceans. Today is contains many information about the marks that are above the sealevel. One of the projects of the OpenSeaMap community is to make sure the underwater is as well known. I will describe what is done, which hardware and which software is developed, what could be some ideas for the Belgian coasts and give some other ideas, what needs to be done.