In oceans throughout the world

All fifty or so species of sea snakes are venomous. The venom is composed of powerful neurotoxins and sometimes myotoxins with a fatal dose being about 1.5 milligrams.

Unlike land snakes, however, sea snakes are not inclined to bite humans, and as such are not harmful unless abused. Most cases of people being bitten by sea snakes involve fishermen bitten when sorting through a catch from a net.