Oceans cover 71% of the earth’s surface with a minimum of 356,000 km of coastline, yet only 2.5% (about 86 species) of the 3364 extant snakes are known to inhabit the oceans on a regular basis. It is unclear whether most of these snakes are spending substantial amounts of time in salt water and are well adapted for life in saline waters, or whether they use behavioral osmoregulation, shuttling between marine and freshwater environments while remaining dependent upon sources of freshwater. Given the low percentage of snake species in the oceans, the physical environment appears to provide challenges for snakes. A survey of lifestyles (habitat use foraging modeþdaily activity pattern þreproductive mode) of 2552 alethenophidian snakes in 459 genera revealed about 362 (14%) species using aquatic environments to varying degrees; only 70 (2.7%) of these are sea snakes (Hydrophiinae and Laticaudinae). Another 65 or more species appear to use brackish water or the ocean. The ancient Acrochordidae contains three extant species, all of which have populations in brackish, marine, and freshwater environments. The Homalopsidae containing terrestrial, semi-aquatic, and aquatic snakes has about 14 species that have invaded brackish and marine waters. The speciose Dipsadidae of the western hemisphere has at least seven species with coastal–marine populations, the cosmopolitan Natricidae has about 24 species with populations using brackish waters but most of these also have populations that primarily inhabit freshwater. The semi-aquatic, African Grayiinae has at least one species that uses brackish water. However, any aquatic or semi-aquatic snake with a coastal population is likely to visit brackish water on occasion. Flooding may move snakes downstream into estuaries, while storm surges, high tides, and rising sea levels (prehistoric marine incursions) may move saline water inland.