During hypoxic events, free-swimming organisms flee oxygen-depleted waters, while slow-moving crustaceans that live along the floor are unable to migrate and often die.

Algae blooms, a sign of water overrich in nutrients, are likely to appear, and fish kills in oxygen-depleted waters are possible, Mr. Sklar said.

This spread of toxic, oxygen-depleted water would have been devastating for marine life, producing widespread die-offs.

Hypoxia may also be the explanation for periodic phenomena such as the Mobile Bay jubilee, where aquatic life suddenly rushes to the shallows, perhaps trying to escape oxygen-depleted water.

She had been holding her breath while working in the hold, to avoid the oxygen-depleted water there, but that hardly added to her comfort.

The quagga mussel is also a suspect in the "dead zone," a 60-by-20-mile plume of oxygen-depleted water in the center of the lake.

African arowanas have air-breathing organs on its branchiae, enabling them to survive in oxygen-depleted water.

These fish have many adaptations that allow them to survive in the oxygen-depleted flood-plain waters.

For example, when a Tetractenos is in oxygen-depleted water, its underbelly will be a darker colour than the usual whitish-cream.

Paleontologists suggest that its giant size was an adaptation for life in the murky bottom waters, where a correspondingly large gill area would have allowed the animal to cope with oxygen-depleted waters.