Frontline warrior in battle to combat river menace

Didymo Dave Cade. Photo / Supplied

Community action can stop didymo spreading through the North Island, says "Didymo" Dave Cade.

The Taupo environmental activist is promoting measures to halt the spread of the unpleasant alga, also called "rock snot", which coats rocks with slippery brown slime.

Summer advocacy rangers from DoC would patrol North Island lakes and rivers, reminding users to "check, clean and dry" anything coming in contact with the water, including fishing equipment, footwear, even the family dog, Cade said.

"Don't worry if you spend a day on a single lake or river, but do 'check, clean and dry' when you move between two or more waterways.

"For example, if some trampers were to walk up a stream bed all day that would be fine. But if they intend to cross a ridge, then walk down another stream bed, they should clean their boots first."

Didymo cannot be removed from a river or lake but can be prevented from spreading between waterways.

Every place it has been found in the South Island has been a human access point to a waterway, and it's thought the alga isn't spread by birds.

"The South Island became contaminated 10 years ago but North Island rivers and lakes tested didymo-free as recently as October," Cade said.

"The South Island has maybe 200 contaminated waterways, but about 400 that are didymo-free - it's far from a lost cause. Our island has been didymo-free for 10 years and we'll keep it that way if we're up for the fight."