Eutrophication refers to the problem of nutrient enrichment of water bodies. The reasons for this are related to the myriad of symptoms that eutrophic lakes, reservoirs, and rivers often exhibit such as unsightly algal blooms, large growths of aquatic macrophytes, excessive accumulations of decaying organic matter, taste and odour problems, decreased deepwater oxygen levels and marked shifts in the structure of the food web including possible extirpations of some fish species and other organisms.