This poster presents an overview of our technique to create detailed 3 dimensional bathymetric and contour maps of marine environments. We use an occupancy grid based representation for the map. The maps are constructed using information gathered by an automated robotic boat mounted with an Imagenex 881L pencil beam sonar. We also present some preliminary work on intelligent exploration strategies for map construction, given the set of constraints on our robotic boat (time, distance, energy, physical constraints). Provision of accurate maps provides invaluable information to marine biologists including water volume, volume changes due to tidal cycles which indicate the amount of bio mass present in the water body and its changes. Using the maps, scientists can determine interesting locations for deployment of sensors for environmental monitoring.