SMHI has developed a model system for water quality calculations on land, in lakes and rivers and in coastal zone waters around Sweden. The system is called HOME Water where HOME stands for Hydrology, Oceanography and Meteorology for the Environment. The focus in this report is to describe the coastal zone model which is the part of the HOME Water system that calculates the state in the coastal zone along the whole Swedish coast. The coastal zone model is a coupled 1-dimensional physical and biogeochemical model. The physical model is called the Probe model and is fully described by Svensson (1998). It calculates the horizontal velocities, temperature and salinity profiles. The surface mixing is calculated by a k -e turbulence model and the bottom mixing is a parameterization based on the stability in the bottom water. Ice formation growth and decay is also included in the model. Probe has a high vertical resolution with a vertical grid cell size of 0.5m in the top 4m. The grid cell size then increases as the depth increases. In the depth interval 4 -70m the cell size is 1.0m, from 70 – 100m it is 2m, from 100-250m it is 5m and if the depth is larger then 250m the grid cell size is 10m. This means that the model calculates the vertical profiles of all its variables and assumes that they are horizontally homogeneous in the studied area. In order to include horizontal variations in a larger area it is divided into several sub-basins. These subbasins are identical to the defined national water bodies according to the Water Framework Directive (WFD). Each sub-basin is described by the hypsographical curve. Connecting sub-basins exchange water and properties through connecting sounds. The biogeochemical model is called SCOBI (Swedish Coastal Ocean BIogeochemical model). In SCOBI nine variables are solved where seven are the pelagic variables: zooplankton, phytoplankton, detritus, nitrate, ammonium, phosphate and oxygen. In the bentic layer the model solves for the two variables nitrogen and phosphorus.