Australia's deadly saltwater crocs are making a dramatic comeback. They're spreading in alarming numbers through the billabongs, rivers and beaches of the Northern Territory. Last year, over 300 had to be removed from the harbour of Darwin, the region's capital. Hundreds of cattle are being killed, and most worrying of all, attacks on people are increasing every year, often in places where crocs were previously unknown. Biologist Adam Britton tries to find out why the crocs have suddenly become such a problem.