Data from monitoring of the dispersion and effects of the hypersaline effluents originated by desalination plants are very scarce. The objective of this paper is to present the monitoring, on time and space, of the brine discharge originated by the Alicante seawater desalination plant (SE Spain). Since the seawater reverse osmosis (SWRO) desalination plant started to operate in September 2003, to the date, three campaigns were made in order to determine the seasonal and spatial distribution of the brine plume and its dilution along the area. One year after the plant operation, the results obtained at these campaigns have shown that dilution of the brine may be lower than the usually accepted and it may affect significant extensions of marine communities. Due to the recent development of the desalination activity in our country the information obtained in this work can be considered really useful for its application to future similar projects in the Mediterranean Sea.