Highly venomous, entirely uninterested in divers, and it comes ashore to digest and shed.
To about 150 cm, pale blue-grey with 20 to 65 black rings, a yellow upper lip and snout, and a flattened paddle-shaped tail. Females are markedly larger than males. It is a sea krait rather than a true sea snake: it retains broad belly scales and can move on land, and it returns to shore to rest, digest, mate and shed its skin.
It hunts eels and small fish in reef crevices, working systematically along a stretch of reef and surfacing to breathe every twenty minutes or so. The venom is a potent neurotoxin, but the animal is not aggressive, its mouth is small, and bites on divers are very rare; they occur almost entirely when a snake is handled or trapped against the body. Divers are frequently followed by one, which is a matter of the snake using them as a moving hunting screen. Recorded from the surface to about 30 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.