The species pictured is a Marsh Snake Hemiaspis signata, it is a venomous Elapid (but not considered extremely dangerous) that feeds on frogs and skinks, they rarely exceed 50cm.
The cream marking with a black upper edge starting at the eye and finishing at the nape is a unique characteristic of this species, it also has a 2nd cream stripe along the side of the bottom jaw. The ventral scales (underbelly) are usually dark blue or grey but it some populations they can also be light yellow or salmon pink in colour. the anal scale is divided.
Another species called the White-lipped Snake Drysdalia caronoides is very similar but it has an unbroken cream stripe with a black upper-edge starting at tip of the snout which progresses along the upper lip and extends down to the beginning of the nape. It has cream or pink coloured ventral scales and a single anal scale.