Litter at sea is an ecological, economic, and social problem that impacts marine environments around the world. To create prevention and mitigation measures to solve this issue, it is necessary to understand the amounts and potential sources of this kind of pollution. Cassino Beach is an extensive ( 220km) sandy beach in Southern Brazil that presents multiple uses, with intense touristic, portuary and fishery activities. A peculiarity of this beach is that motor vehicles can transit on the sand strip, increasing beach use and possibly litter disposal. Seasonal touristic activities and the large extension of the beach allow comparisons of litter amounts, composition and possible sources between seasons and sampling sites. Sampling was done over 27 months at four points at the beach (2 urban, 2 non-urban); at each site, litter (¿2.5cm) present in three 200m2 transects was collected and evaluated. A total of 19,457 items were collected, and plastic composed 88% of litter. Paper, metal, and cloth items were also present, but in low amounts. In the plastic category, fragments and cigarette butts were the major types of litter, with abundances of 28.4% and 17.0% respectively. Urban sites presented higher amounts of litter than non-urban sites, and beach user-related litter source was more common in urban sites, emphasizing the contribution of beach use in marine litter deposition. Corroborating this, the summer season presented the highest litter density, and undetermined and/or beach use related sources were dominant in all sites and seasons. Mapping the predominant material, types and sources of marine litter creates important baseline data that can contribute not only to beach monitoring, but also to the development of litter reduction strategies.