Enhydris enhydris
Malaysia (© Tom Charlton) 
Lake Songkhla (© John Murphy) 
Vietnam (© Alex Krohn) 
captivity (© Wolfgang Wuster)
English name: Rainbow Water Snake (aka “Rainbow Mud Snake”, “Striped Water Snake”, “Schneider’s Water Snake”)
Scientific name: Enhydris enhydris
Thai name: งูสายรุง (Ngu Sai-rung), งูปลา (Ngu Plaa)
Description: To 97cm long. Robust midbody with relatively slender neck and forebody. Olive-brown color with a creamish stripe (often with red midline) just above the ventrals and often two light yellow or reddish dorsolateral stripes higher up. Some individuals have a darker dorsal stripe. White to yellow belly with a dark stripe or dots down the center.
Relevant scale counts: 21 midbody scale rows, scales are iridescent and have striations. 153-174 ventral scales.
Similar Species: Mekong Mud Snake has dark markings in addition to light stripes and less than 153 ventral scales.
Chanard’s Mud Snake has dark spots along its side, lacks striations on the scales, and has less than 125 ventral scales.
Jagor’s Water Snake has dark blotches running down its side, lacks stripes, lacks striations on the scales, and has less than 127 ventral scales.
Sunbeam Snake has a wedge-shaped head and lacks colored lines.
Red-tailed Pipe Snake lacks colored lines, is more uniform in girth, and has a barred underbelly.
Range: From India east through southeast Asia and south into Indonesia.
Habitat: A highly aquatic species that is always in or near wetlands. Is found in a wide range of aquatic habitats, including manmade lakes and ponds. Spends most of its time hunting just off the shore, taking advantage of the tangles of vegetation in the mud at the water’s edge. Is rarely seen in the open, preferring to remain underwater or within vegetation mats and tangles. Does not tolerate brackish water.
Place in the ecosystem: Primarily feeds on fish, but also frogs and tadpoles. Is eaten by larger snakes, large fish, monitors, and wading birds.
Danger to humans: Like other water snakes in its family, the Rainbow Water Snake has a very mild rear-fanged venom that does not pose a threat to humans though it may lead to pain and swelling.
Conservation status and threats: Due to its ability to survive in a wide range of habitats and tolerate human encroachment, the Rainbow Water Snake is a common species in Thailand. However, a recent increase in the harvest of water snakes in Cambodia (for food, skins, and crocodile feed) has led to declines in some populations there. As many as three million Rainbow Water Snakes are estimated to be captured from the Tonle Sap Lake every year.
Interesting facts: Asian water snakes have a number of specialized traits to support their aquatic lifestyle. These include eyes positioned on top of the head (to see prey and threats while remaining underwater), nostrils that can be closed while underwater, and young that are born live (eliminating the need for a dry place to lay eggs).
References:
The IUCN Red List: Enhydris enhydris
Reptiles Magazine: Mud Snakes
Semi-aquatic Snake Communities in the Central Plain Region of Thailand
The Ecology of the Water Snakes of Ban Tha Hin, Songkhla Province, Thailand
A Checklist and Key to the Homalopsid Snakes with the Description of New Genera
A Photographic Guide to Snakes and Other Reptiles of Peninsular Malaysia, Singapore and Thailand
A Field Guide to the Reptiles of South-East Asia
A Field Guide to the Snakes of South Vietnam
Reptiles and Amphibians of Thailand 