Freshwater Snake (Keelback Snake)

Tropidonophis mairii

Freshwater Snake (Tropidonophis mairii) Head of Freshwater Snake, Tropidonophis mairii showing distinctive dark edging between lip scales.
Photograph by Richard Jackson.
Tropidonophis mairii distribution Tropidonophis mairii feeding on introduced Cane Toad. Freshwater Snake, Tropidonophis mairii, feeding on introduced Cane Toad.
Photograph by Steve Wilson.
Freshwater Snake, Tropidonophis mairii Freshwater Snake, Tropidonophis mairii
Photograph by Richard Jackson.


The Freshwater Snake (also known as the Keelback) is olive brown with irregular dark cross-bands.  The body scales are strongly keeled, producing ridges that run along the snake’s body.  Flecks of pale skin can often be seen through the scales.  The belly is cream and usually flushed with a pink or orange tinge along the edges.  Dark bars can be seen between the sutures on the upper lip scales.  This species grows to 75 cm.  Midbody scale rows 15 (rarely 17); ventrals 130–165; anal divided; subcaudals divided 50–85.


Found in coastal areas of northern Australia from northern New South Wales to the Kimberley, Western Australia.


Lives in well watered situations along creeks and in swamps but also found in eucalypt forests, heaths, pastures, parks and suburban gardens. Habits:  This species is active both day and night.  It is usually found at ground level, but can climb well (a specimen was observed 5 m up a melaleuca tree in a swamp on Cape York Peninsula).


A non-venomous, inoffensive species.


Feeds mainly on frogs, but fish, reptile eggs and mammals are also taken.  This species is one of the few Australian vertebrates to prey successfully on the introduced Cane Toad.  However, attempts by this snake to eat large toads sometimes have fatal consequences for the snake.


This species lays 5–12 eggs.  The hatchling snakes are around 15 cm from the tip of the snout to the base of the tail (snout-vent length).

Similar species:

This snake is most similar to the venomous Rough-scaled snake but is distinguished from this species by having divided subcaudal scales and only 15 midbody scale rows.  The Rough-scaled snake has single subcaudals and 23 midbody scale rows.  Unlike Freshwater Snakes, Rough-scaled Snakes have no pink tinge along the edges of the belly scales.

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