http://www.pantheon.org/articles/m/mami_wata.html

Mami Wata is a water-spirit, sometimes described as a mermaid figure, who can found throughout the western coastal regions and into central Africa. Mami Wata is described as having long dark hair, very fair skin and compelling eyes. Although she may appear to her devotees (in dreams and visions) as a beautiful mermaid, complete with tail, she is also said to walk the streets of modern African cities in the guise of a gorgeous but elusive woman. She is interested in all things contemporary: some of her favorite offerings include sweet, imported perfumes, sunglasses and Coca-Cola. Nonetheless, the spirit appears to be related to other water spirits (known in Igbo, a language of southeastern Nigeria, as ndi mmili) who have a much longer history on the continent. Mami Wata's colors are red and white. Those she afflicts with visions and temptations, and who experience her as an obsession or an illness, may wear the red of sickness and dangerous heat. Others who have a more positive orientation towards the spirit may show their blessings by wearing white. Most devotees wear a combination of red and white clothing. Mami Wata is also said to have a number of avatars on earth--mortal women who have the same look as the deity and who act as her "daughters." Mami Wata may give wealth to her devotees, her "daughters" or to her (male) spouses, but she is never known to give fertility. Some Igbo stories suggest that the fish under the waters are her children, and that she uses them as firewood.

Mami Wata is sometimes seen as a metaphor for modern African conditions -- having the knowledge of global wealth and the desire for large-scale consumption, but lacking the actual wealth or access to the world's wealth that would enable Africans to participate in that system. A number of Africanist art historians have written about Mami Wata, notably Henry Drewal, as have anthropologists like myself. She is the subject of local poetry, song, paintings, carvings and now film.