Plastics are one of the most common and persistent pollutants in aquatic ecosystems worldwide. They have significant harmful effects on both marine and freshwater ecosystems. Numerous investigations were made in marine ecosystems but too little is known of the freshwater ecosystems, and for this, the generation of basal information is a priority. From the continent, plastic waste is transported through river systems (e.g. rivers and streams) and urban drains, eventually reaching coastal areas and oceans. When analyzing these contributions, it is essential to consider the characteristics of the lotic system analyzed at a basin scale, including human activities in the area of influence. The Maldonado stream is the main fluvial system in Maldonado, Uruguay, a direct tributary of the Atlantic Ocean. In its basin, this stream crosses agricultural and livestock areas, and borders the cities of San Carlos and Maldonado. These different activities, and especially urban areas, can contribute with various pollutants, among which plastic waste stands out. The aim of this study is to carry out the first detailed analysis of presence, distribution, and transport of microplastics along the Maldonado stream basin. Covering from the upper of the basin to the mouth of the Maldonado river in the Atlantic Ocean, surface water was sampled using a motor pump and a skimmer (aprox. 1500liters) in 5 sites throughout 2019 (seasonal frequency). Densities were determined considering fibers larger than 0.5mm and fragments larger than 0.1 mm. All these items were classified and quantified according to their type, size and color. The first results show a total density of 323 items.m-3 in May and 236 items.m-3 in July, with fibers as the most represented type of MP in both samples (93%and 7%, 90% and 10%, respectively). Our results provide the first baseline information of microplastics on this coastal stream basin.