Water completely devoid of oxygen is called anoxic.
Salon(Nov 03, 2016)
The mat had previously covered the seabed like a coating of plastic wrap, leaving the underlying sediments largely anoxic and off limits to animals.
Nature(Feb 15, 2016)
He was also diagnosed with anoxic brain injury brought by prolonged oxygen deprivation.
Washington Times(Oct 01, 2015)