Abstract
Observations were made at 101 localities and the area was divided into 4 sub-areas, each with its characteristic floristic features. A brief general description of the vegetation of the different sub-areas is given. The Oslofjord previously was subjected to algological investigations by Sundene (1953) and Grenager (1957) and the results of the present survey are compared with their results. The survey contains descriptions of seasonal and annula variations in the vegetation throughout the whole area. On the basis of the available data on salinity, temperature, currents, pollution and other ecological factors, the distribution patterns of the various benthic algae are discussed. Finally, there is a floristic list with information on life cycle stages of the various species.