"Rivers in the southern hemisphere are particularly at risk to new introduction and invasion. Appropriate agency personnel in Australia, Argentina, Chile and Peru should be notified and made aware of the potential ecological damage and urgency of implementing decontamination procedures." (page 11)
FIGURE: Map of the world showing regions where suitable stream habitats for D. geminata are located. (Map by Kris McNyset, US Environmental Protection Agency).
The government of Australia took the 2007 warning seriously and prevents Didymo infected items from entering the country:
What are the risk items?
Didymo can survive in damp moist conditions and is often inadvertently carried in sporting equipment and fabrics such as:
fishing equipment: rods, reels, bags, rope, nets, knee guards, gators, felt soled shoes, waders, recreational and watersport equipment: wetsuits, neoprene socks, waterskiing and wakeboarding equipment (including components) buoyancy vests, kayaks, canoes and other watercraft, paddles, spray decks, spray skirts, soft foam handles, hiking gear and swimwear.
What can you do before returning to Australia?
All travellers carrying such items need to thoroughly clean and completely dry all components, inside and out. It is also a good idea when you’re packing your bags to ensure all risk items can easily be accessed when required for inspection.
What to do when arriving in Australia?
It is important that you:
Declare all items on your Incoming Passenger Card
Present all items to an AQIS Officer for inspection.
What happens next?
The AQIS Officer will inspect all items to assess the level of risk each item presents. Once assessed, the AQIS Officer will advise you whether or not the item needs to be treated before it can enter Australia. If it requires treatment, it will be treated in the nearest AQIS approved treatment facility, subject to availability; which may result in delays in getting items back. If the risk item can not be treated it will need to either be destroyed or re-exported. All treatment, destruction or re-exportation costs are at the owner’s expense.
More here: http://www.daff.gov.au/aqis/travel/entering-australia/didymo/didymo2
Australia border control video here: http://www.youtube.com/watch?v=8xxWI2WGxyY