We have just sent two whitewater kayaks to Oz (via a re-location company) and they are currently held up in Oz quarrantine due to potential Didymo issues (along with everything else of ours).
No word yet on time or cost to have them released (will advise the outcome when we know), but a timely reminder to all that you may now encounter issues with taking your kayak to Australia. This may or may not occur if your boat comes with you as checked luggage.
Suggest the usual: Thoroughly clean the kayak with disinfectant, leave in the sun to dry for a couple of days, etc (as per DOC guidelines). For un-accompanied boats suggest a cleaning certificate of some sort, and / or notice stuck on boat to say it has been cleaned properly and not used on didymo infected waters (if you know for sure that is).
I've heard horror stories of Oz MAF charging 300$ to clean tramping boots and tents - on a per item basis...(probably deserved it if they were not cleaned, but indicates that it could cost a lot to have your kayak cleaned).