Artificial gills are hypothetical devices to allow a human to be able to take in oxygen from surrounding water.
One proposed method is the use of liquid breathing with a membrane oxygenator to solve the problem of carbon dioxide retention, the major limiting factor in liquid breathing.
[1][2][dubious – discuss] It is thought that a system such as this would allow for diving without risk of decompression sickness.
The amount of dissolved oxygen in water varies, but on average is 7.6mg per liter.
Seawater in tropical regions with abundant plant life contains 6–8 mg (0.093–0.123 gr) of oxygen per liter of water.