KEY POINTS:
Holidayers returning from the South Island have been appalled at the spread of didymo weed in sparkling rivers. They say the invasive algae looks not so much like rock snot, as it is commonly called, but like used toilet paper.
At the same time, overseas anglers returning from South Island visits have spoken in glowing terms of Biosecurity New Zealand's summer campaign to keep didymo out of the North Island and thus out of two of the world's great trout fisheries, Rotorua and Taupo.
The campaign, which runs until June, has Biosecurity NZ staff targetting passengers at the interisland ferry terminals and at international and domestic airports, paying particular attention to travellers with boats and kayaks, fishing gear and other aquatic equipment. Their essential message is one of personal responsibility: Check, clean and dry all equipment between waterways.
A didymo DVD is played on the ferries and Biosecurity staff often join the sailings to speak to passengers about the river cancer. Cleaning stations are set up in Picton as well as spraying units at the ferry terminal, complementing cleaning facilities set up around the South Island by other groups.
At the international airports, MAF staff are on the lookout for travellers coming through with aquatic equipment.
Since it was discovered in Southland in 2004, didymo has been found at 51 locations on 31 rivers and lakes throughout the South Island, the three most recent this year being in Lake Wakatipu, which is fed by four affected rivers, and in the Pelorus and Speargrass Rivers at the top of the South Island.
Left to spread unncontrolled, didymo forms dense mats which destroy ecosystems. Rivers cease to be places of scenic splendour and they become unfishable. The seriousness was best summed up by Biosecurity Minister Jim Anderton when he told Parliament: "... there is no treatment or technology for controlling didymo anywhere on the planet", and went on to say that New Zealand was doing more research and monitoring of the algae than any other country.
New Zealand scientists' efforts to combat didymo are being watched with great interest around the planet. Niwa scientists have developed and tested a copper compound on a small tributary of the Mararoa River in Southland, and early results have been encouraging.
It appears the compound kills the invader's cells without harming rainbow trout and with only minimal effects on other river life. Monitoring of the site is continuing and the results could be completed next month.
It is frightening to think that in an increasingly tourist-driven, shrinking and polluted world, didymo may not be the last of the foreign river invaders. What else is out there waiting its chance? And what if - as some internet reports have speculated - it is carried by birds?
