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The Nile monitor (Varanus niloticus) is a large member of the monitor family (Varanidae) found throughout most of Sub-Saharan Africa and along the Nile. The population of West Africa forests and savannahs is sometimes recognized as a separate species, the West African Nile monitor (V. stellatus). Other common names include the African small-grain lizard, water leguaan  or river leguaan (leguan, leguaan, and likkewaan mean monitor lizard in South African English, and can be used interchangeably). In Kenya there 2 species of Monitors , the other one being savannah monitor (Varanus exanthematicus).

Nile monitors can grow to about 120 to 220 cm in length, with the largest specimens attaining 244 cm.  In an average-sized specimen, the snout-to-vent length will be around 50 cm.  In body mass, adults have been reported to vary widely, one study claiming only 0.8 to 1.7 kg, others state weights ranging from 5.9 to 15 kg  in big monitors. Variations may be due to age or environmental conditions. They have muscular bodies, strong legs, and powerful jaws. Their teeth are sharp and pointed in juvenile animals and become blunt and peg-like in adults. They also possess sharp claws used for climbing, digging, defense, or tearing at their prey. Like all monitors, they have forked tongues, with highly developed olfactory properties. Their nostrils are placed high on their snouts, indicating these animals are highly aquatic. They are also excellent climbers and quick runners on land. Nile monitors feed on fish, snails, frogs, crocodile eggs and young, snakes, birds, small mammals, insects, and carrion. They are also the second largest reptile in the Nile river.

Source : Wikipedia