Azolla is a genus of aquatic ferns that is found all over the world in tropical and freshwater. Depending upon its location, this fern can be either beneficial or a nuisance. The Azolla fern is considered a weed when its rapid growth congests waterways and when its biomass increase leads to eutropaication in closed bodies of water. Azolla are known for their ability to harbor nitrogen-fixing bacteria, but this would not be an advantage in nitrogen-rich wastewaters. The azolla contains chlorophylls a and b while the alga contains chlorophyll a and phycobilins. Both partners contain carotenoids. The color of azolla is more olive-green than that of the duckweeds, and their fronds are bordered with a pink anthocyanin pigment. One of the pigments produced by a group of microscopic organisms accounts for the reddish color often seen in Azolla plants.