Hypoxia

• A low oxygen condition in the water that may occur where a nutrient-laden free-flowing body of water (like a river) enters a lake or ocean. The high nutrient content promotes rapid growth of plankton/phytoplankton that subsequently die and, in the process, consume large amounts of oxygen (see biochemical oxygen demand) . While fish and shrimp can migrate away from a hypoxic area, less mobile bottom-dwelling organisms are unable to escape. A Mississippi River/Gulf of Mexico Watershed Nutrient Talk Force under the leadership of the Environmental Protection Agency (comprised of representatives from the scientific, economic, ecological and agricultural communities) is investigating the recurring and increasingly large hypoxia problem at the mouth of the Mississippi River. Currently, scientists believe nitrogen making its way into tributaries that flow into the Mississippi River, and eventually the Gulf of Mexico, causes the hypoxia condition.
• low oxygen pressure due to being at high altitude. Source: Anthromorphemics

A condition in which there is a decrease in the oxygen supply to a tissue. In cancer treatment, the level of hypoxia in a tumor may help predict the response of the tumor to the treatment.