Algae may cost hundreds of millions

The unchecked spread of didymo algae in New Zealand waterways could cost the country more than $285 million.

The figure was arrived at as a worst-case scenario in a report on the weed from the New Zealand Institute of Economic Research.

It looked at the potential impacts of didymo if there was no government intervention to control its spread, over the eight years to 2011-12.

The invasive algae would have a big impact on tourism, fishing, municipal, industrial and agricultural water intakes and recreational values.

A low-impact scenario would have a financial impact near $58 million and would see a high and persistent biomass of didymo in high-risk river reaches.

The medium-impact scenario would see the addition of moderate and occasional biomass in medium-risk river reaches and low biomass in lakes, and could cost New Zealand more than $167 million.

The report, to Biosecurity New Zealand, says the high-impact scenario would see high and persistent biomass in high and medium-risk river reaches, and moderate and occasional biomass in lakes.

"Total impacts are dominated by reduced recreational values, loss of existence values associated with extinction of native species and reduced tourism expenditure, followed by increased costs for water intakes and reduced local and national existence values," the report says.

Total impacts are greatest in the North Island and central South Island.

"Although the lower South Island has the largest amount of highest risk environment for survival of didymo and is where impacts occur earliest, the central South Island and North Island have substantially larger human populations to suffer reduced recreation and existence values," the report says.

Didymo was discovered in two southern river systems in 2004 and had probably been in them for up to two years, scientists say.

It has caused increasing concern overseas for its ability to spread rapidly, choking waterways and killing invertebrate life essential for fish survival.

Since then the whole of the South Island has been declared a "controlled area" for the algae.

Travellers and freight companies crossing Cook Strait from the South Island to the North Island must clean items that have been in lakes or rivers.

People in the South Island will have to clean all items - clothing, rods, waders, boats and vehicles - which have been in a stream, river or lake, before they enter another waterway.

* The threat: The invasive algae didymo if left unchecked could pose a substantial economic burden on New Zealand within a decade.

* The response: Eradication may not be possible and the cost of its spread could run into millions of dollars as it chokes waterways and destroys invertebrate life essential for fish survival.

- NZPA