KEELBACK OR FRESHWATER SNAKE Amphiesma mairii (Gray, 1841)
Common along the coasts of Queensland, The Northern Territory, the Kimberleys in Western Australia and nearby areas, the Keelback varies in colour from grey, green, red, olive, red, black or something between these colours. Often more than one colour phase occurs within a single locality.
Averaging about one metre, this harmless snake is commonly confused with the dangerous Rough Scaled Snake Tropedichis carinatus.
The scalation of the Keelback is strongly keeled, with 15-17 mid body rows, 130-165 ventrals, divided anal, and 50-85 divided subcaudals.
This snake is usually found in close proximity to water, where it feeds exclusively on frogs and the introduced Cane Toad (Bufo marinus). This snake appears to have immunity to the venom of the Cane Toad, unlike most other reptiles. When feeding, this snake usually but not always, swallows frogs and toads, hind quarters first.
When specimens are caught, they will often try to shake themselves loose, even by shedding their tail, which will not regenerate.
The Keelback is both diurnal and nocturnal.
Mating occurs in winter and spring with 6-12 eggs being laid in January and February. These hatch about 70 days later. Hatchlings measure 14 cm.

The above was from the book Australian Reptiles and Frogs by Raymond Hoser and now available on a fantastic CD-Rom along with a vast amount of other information, papers and the like on reptiles, frogs and other wildlife.