The slender-necked sea snake (Hydrophis coggeri), also known commonly as Cogger's sea snake, is a species of marine venomous snake in the subfamily Hydrophiinae of the family Elapidae.

The species is native to waters around western Australia and the southern Pacific Ocean.

The specific name, coggeri, is in honor of Australian herpetologist Harold Cogger.

[3] H. coggeri is found in marine waters around Fiji, the Loyalty Islands, New Caledonia, and western Australia.

[2] The preferred natural habitats of H. coggeri are coral reefs and seagrass beds, to a depth of 45 m (148 ft).