Surface water refers to water that flows over, or rests on, the surface of a land mass. It is found in rivers, lakes, wetlands, seas and oceans or stored in reservoirs or other impoundment structures. Surface water is naturally replenished by precipitation and naturally lost through evaporation and infiltration into the ground. In the Lake Chad hydrographic basin, all surface water flows into Lake Chad, which is the outlet. As it flows towards the lake, the water picks up particles of sediment, organic matter, chemicals, etc. along the way. The course the water follows towards the lake, and therefore its quality and quantity, is determined by land use, human activities, infrastructure and floodplains. The Lake Chad hydrographic basin is essentially formed by the Chari-Logone drainage basin and the Komadugu-Yobe drainage basin. There are, however, also small catchment areas in the state of Borno in Nigeria, with streams that feed Lake Chad.