Rivière Noire or Black River is a district on the western side of the island of Mauritius. Rivière Noire translates to Black River. This region receives less rainfall than the others. The district has an area of 259 square kilometres (100 sq mi) and the population was estimated to be 80,939 as of 31 December 2015. It is the third largest district of Mauritius in area, but the smallest in terms of population. The district is mostly rural, but it also include the western part of the city of Port Louis and western part of Quatre Bornes.

Port Louis is the capital city of Mauritius. It is mainly located in the Port Louis District, with a small western part in the Black River District. Port Louis is the country's financial and political centre, and the most populous city. It is administered by the Municipal City Council of Port Louis. According to the 2018 census conducted by Statistics Mauritius, the population was 147,066.