Crocodiles can be notoriously difficult and dangerous to photograph if, like me, you really want to see the "whites of their eyes". Safest approach is in a boat when there is a chance that they will not think that you are a person - just an odd shaped boat. The trouble with this approach is that the only kind of boat that is likely to allow you to get close will be of a size that a decent croc can overturn. Unfortunately anything that lives in the waters of Africa and can eat you can also swim faster than you - even if you were Olympic trained!
If you're working a river or lakeside bank on foot then you certainly stand a chance of creeping up un-noticed if your bushcraft is up to it. The potential problem with this line of approach is that you can all too easily stumble on a nesting or resting croc concealed in the bankside vegetation. This is one of the only occasions on which I can be persuaded to get "my kit" - or part of it anyway - off in public. You need a decent stick about six feet long to the end of which you can tie your shirt. Holding this out in front of you as you walk along the waters edge will hopefully give a croc a primary target to lunge at when he comes at you like a rocket, leaving you time to "do a runner".
My advice to you if confronted by this scenario is - be prepared to sacrifice the shirt!