The answer is; Dead Zone
These areas have anoxic condition means they have very little to zero dissolved oxygen hence cannot support marine/aquatic life. This is as a result of eutrophication caused by algae blooms. This phenomenon is brought about by pollution of these water reservoirs. These algae bloom take up all the oxygen in the water during their mass decomposgion hence leave no dissolved oxygen for the rest of the marine life.
The answer to the fill in the blank question is Anoxic conditions
