Following one of the worst rainfalls on record on April 27, Hydro's part-owned Alunorte alumina refinery in Brazil experienced an overflow of one of its rainwater drainage channels.
The incident led to bauxite deposits seeping into the Murucupi river, colouring the water red and prompting an investigation by Alunorte in collaboration with local authorities.
The region saw 105 millimetres of rain in just 90 minutes on April 27, equal to almost one-third of what is normal in the entire month of April.
Although preliminary test results of the Murucupi showed that the spill posed no significant threats, further tests are being made to ensure human health and aquatic life as the spillage contained traces of caustic soda used in the process of refining alumina from bauxite.
Alunorte, which has been fined because of the red mud spill, is in dialogue with authorities as well as the local community about the incident, and also met local and regional media on April 30.
The company has already increased the height of the drainage channel that was flooded in the unusually strong rainfall to prevent spillage from occurring in the future.