Sopot?s intensively used sandy beach was studied to assess organic matter deposition and swash water filtration through the sediment on the water line. The swash water contained from 4 to 80 mg Total Suspended Matter (TSM) per dm3, 3 to 12% of it was organic. Phytoplankton ranged from 1 to 15 million cells per dm3, depending on the water turbidity and contained a mixture of pelagic and micro-phytobentic taxa. Plankton larvae and Rotatoria dominated the animal biomass. In the process of wave filtration through the sand all planktonic animals were retained in the sediment, while a number of meiofaunal Nematoda and Ciliata were actively transported (?washed out?) from the upper sediment layers. Macroscopic particle (filamentous algae) deposition in May ranged from 20 to 1000 g POC m-2 per day. Nutrient concentrations were higher in the interstitial water than in the swash water, for most of the year. Hence, we suppose that the Sopot municipal beach serves as a nutrient source for coastal waters.