If sea water on a fire is not an issue, however no doubt the greenies would make it one, but given we have a vast coastline stretching very close to the areas in which wild fires are prevalent, would that not make a case for the Russian Be 200 amphib?
It can scoop up 12 tonnes of water in 14 seconds, carry up to 40 passengers, cruises at 300 kts and has a ferry range of 1800 nm. It can operate off a 1.5 meter sea state, 2.5 meters deep.
It is also capable of being configured for other tasks such as search and rescue, marine surveillance or as a freighter.
A series of boat ramps in our more sheltered bays, or expansion of existing ones could provide forward bases for refuelling and servicing.