Almost two dozen scientists from around the world are issuing a warning about an often-overlooked side effect of climate change and pollution.
They say oxygen is disappearing from increasingly large areas of ocean and threatening marine life.
Researchers say in a paper published this week that the problem has been growing since the 1950s, and 4.5 million square kilometres of coastal and deep-sea water is now affected.
That includes oceans off Canada's West Coast and in the St. Lawrence Seaway.
The research was sponsored by an international body affiliated with UNESCO, the United Nations' scientific and cultural body.
