This study aimed to investigate the behavior of organic ultraviolet (UV) filters released by recreational activities along the Japanese coastline. Seasonal variations of organic UV filters in seawater were investigated at four different recreational beaches (Mogushi, Wakamiya, Tsurugahama, and Otachimisaki beaches) in both summer (July through August) and winter (December). Moreover, short time scale diurnal changes were monitored at Otachimisaki beach in summer. Of the four sunscreen agents tested in this study, two agents-2-ethylhexyl-4-methoxycinnamate (EHMC) and 2-ethylhexyl salicylate (EHS)-were detected in all samples, whereas octyl-dimethyl-p-aminobenzonic acid and 3-(4-methylbenzylidene)-camphor were lower than detection limits. In particular, EHMC, one of the most popular organic UV filters, was dominant. The highest concentration of EHMC was observed at 1,080 ng L(-1), a level that exceeds those of previous studies. Both EHMC and EHS concentrations showed significant (p < 0.05) seasonal variations with advancing summer suggesting direct input from recreational activities. The subsequent examination showed short time scale diurnal changes of organic UV filters on the beach. The results showed that diurnal changes in EHMC concentrations were correlated to the number of bathers. EHMC concentrations increased during the afternoon and decreased during the night, although complete attenuation during the night did not occur. EHMC persists along the coast due to low mobility and may persist the next day. This is the first study to show the natural attenuation behavior of organic UV filters along recreational beaches.