Dolphins in Lake Retba or Lac Rose. The lake lies north of the Cap Vert peninsula of Senegal, north east of Dakar. Depending on the time of day, the lake changes colour from a light purple to a deep scarlet pink. The unusual colouring of the water is caused by harmless halophilic bacteria that thrive in the lake’s high-salinity environment. The color is particularly visible during the dry season.