Sinonatrix percarinata percarinata (Boulenger, 1899)
Mountain Water Snake 烏游蛇
(Non-venomous)

Average 70 - 90 cm, may grow up to 110 cm.

Back colour dark brown or olive brown, with a maximum of 36 black or brownish bands forking dorsally.
Bands may not be obvious on top of dorsum, but are clearly marked with pale borders on the lower flanks.
Ventrals whitish or greyish, and have dark incomplete bands.
Flanks of juveniles pinkish, with sharp black bands, but this bright coloration fades with age.
Labials and side of neck yellow. Tail long. Dorsal scales strongly keeled.

Inhabits elevated aquatic habitats, from moderate to steep hill and mountain streams that have cascades, large pools of varying depth and moderate to swift current.

Usually nocturnal. A strong swimmer, most often found swimming in stream pools at night or inside catchwaters.
Juveniles are known to be somewhat terrestrial, leaving streams and travelling overland.
An aggressive snake, which bites readily when caught.
Like Diamond-backed Water Snake (Sinonatrix aequifasciata), is able to climb vegetation, but these two species rarely occur concurrently.

Feeds on frogs, fishes and tadpoles.
Some studies showed that this snake usually swallows frogs from behind.

Oviparous. A single female was reported to have 6 eggs.

First recorded in Hong Kong in 1970.
Widely distributed but uncommon in the central, western and southern New Territories.
Uncommon and has not been recorded on Lantau Island or Hong Kong Island.
Occurs also in southern China, and from northern Burma to Vietnam.