Where can hypoxia occur?

Hypoxia occurs naturally in many aquatic environments throughout the world, such as in deep basins in the ocean. Hypoxic waters have occurred throughout history, but they are occurring in shallow coastal and estuarine waters more frequently as anthropogenic (i.e. human) sources and inputs of nutrients increase.

When does hypoxic hypoxia occur?

The effects of pure hypoxia on the brain (hypoxic hypoxia) are observed in high altitude sickness. Several days after ascending rapidly (usually to altitudes of 8,000 to 12,000 feet), headache, insomnia, anorexia, nausea, vomiting, and impaired cognitive function may occur.