World s Biggest Reptiles Beware! The saltwater croc may grow to 7 metres (23 feet) long and inhabits both sea and rivers; a hefty anaconda can weigh over 250 kg (550 Ib) and stretch out more than 8.8 metres (29 feet); and the Gaboon viper has the largest fangs of all, at 5 cm (2 in) long! There s much more... Make way for the heavyweights!