text: Dead zones can be classified by type, and are identified by the length of their occurrence:
  * Permanent dead zones are deep water occurrences that rarely exceed 2 milligrams per liter.
  * Temporary dead zones are short lived dead zones lasting hours or days.
  * Seasonal dead zones are annually occurring, typically in warm months of summer and autumn.
  * Diel cycling hypoxia is a specific seasonal dead zone that only becomes hypoxic during the night
  The type of dead zone can, in some ways, be categorized by the time required for the water to return to full health. This time frame depends on the intensity of eutrophication and level of oxygen depletion. A water body that sinks to anoxic conditions and experiences extreme reduction in community diversity will have to travel a much longer path to return to full health. A water body that only experiences mild hypoxia and maintains community diversity and maturity will require a much shorter path length to return to full health.