Depends where and how you It will be fishing. A floating line would be ok in shallow creeks and flats whilst a sinking line would better suit if casting into the snags in deepish water. The key will be to get the fly past the Barras nose. Take both! Chasing barra in july is the worst possible time to be targeting Barra as it will be basically too cold for any great fishing. But if your goal is to simply acheive a barra on fly it is possible, maybe try some of the billabongs. Or go when they are biting, during the warmer months  

 Thanks for the advice yeah will be fishing creeks and flats at Melville Island fingers crossed anyway mite be lucky?

 Thanks for the advice yeah will be fishing creeks and flats at Melville Island fingers crossed anyway mite be lucky?

Id use a floating line if fishing the flats. you can cast popper flies into the shallows with ease on relatively short leaders, say 6 feet and you should also be able to entise some big threadfin as well. Ive never fished there but it will be a case of working the last of the runouts i would imagine, and first of the run in. Should be heaps of Trevs and Queenies i would think. Again floating lines will be the easiest option for them.

Personally I'd be chucking around a rio tropical I/I. 

It's a full inter that is well tapered for short & long casts.

You can still use poppers with it but you will have to use a doublehand retrieve straight after the fly has landed and strip really quick.

You should really give us more info on the rod (weight) you intend to use as this can alter the line choice somewhat. Say for a 10 or above a shooting head might even be an idea.

What flies will you be using too? Things & Clousers?

 Yeah have made my mind up to go with Rio WF10 Intermidate. Will be yousing dicevers, pink things and dalhberg divers. My set up is Lamson WaterWorks reel 10 weight and Hardy Rod.