Deep water has little or no dissolved oxygen.
Eutrophication is currently one of the most serious pollution problems in America. The original condition of most bodies of water is oligotrophic. This term refers to bodies of water that are low in nutrients. In turn, submerged vegetation rooted in the soil can flourish. In natural ecosystems, like a forested ecosystem, nutrients are recycled in the soil, going from soil, to trees, to detritus, and back to the soil.