No faster than anywhere else !
He must have been camping with other people and perhaps he just "went for a quick walk". That would explain why the alarm was raised, and perhaps why no shoes etc

(For some reason quite a lot of people like to go bare foot ... In some places it is quite wet with lots of water to cross, plus it can be hot and humid although no so much this time of year)

As for the swimming, the Jardine River is prime croc country !