Help coming for didymo rivers

An out-of-the-box approach to a pest threatening to devastate native fish stocks in some of the South Island’s most iconic rivers has been developed by a young Kiwi entrepreneur.

Logan Williams, 23, has created a way of converting the pest, an algae known as didymo or ‘rock snot’, into 100 per cent recyclable paper, fabric or bioplastic, a discovery that has potential to help clean up waterways.

Perfected during his time as a science student at the University of Canterbury, his invention was named as a regional finalist in the 2019 NZ River Awards.

Didymo is an invasive algae which attaches itself to rocks in fast-flowing streams creating dense sludge-like globs (known as benthic mats) on river bottoms and riverbanks. By affecting the organisms fish feed on, it can devastate native fish populations, suffocate waterways and have a big impact on wildlife, recreation and boating.

Williams, a keen fisherman, says when he was growing up he saw first-hand the waterways he loved becoming infected with the “disgusting brown sludge” and began to notice fishing was worsening as the number of native fish rapidly reduced.

In comments to the award organisers, the Cawthron Institute, he says: “Over a 10-year period I could see more and more thick brown sludge, sometimes aptly called ‘rock snot’.

“Once it’s established it just takes over everything and the river effectively dies,” he says. “It was affecting river after river from the Rangitata to the Tekapo and devastating native populations in the process. Unfortunately for us this stuff thrives in cold, clean and low nitrogen water, so the South Island’s climate is perfect.”

While at university studying science and psychology Williams was able to create biodegradable material from didymo, synthesizing it into paper, fabrics and bioplastic - demonstrating it can be sustainably removed from the environment.

“Didymo is horrible and, as it was a problem close to my heart, I wanted to help people and rivers,” he says. “I was angered at seeing them in such a mess; I caught my first fish as a three-year-old and can still recall the feeling of excitement.”

Williams undertook comprehensive research into the engineering of didymo, conducted commercial trials and generated public awareness about the invasive organism. Through trial and error, solid science, spending hours waist deep in freezing rivers and doing laboratory tests he was able to create the new material.

The didymo solution - one of 150 inventions to Williams’ name - has been fully commercialised by Biome Innovation, the company he founded to create the material. Williams received support from a number of organisations including the University of Canterbury, New Zealand Merino Company, Department of Conservation, Kathmandu, the Projection Room, Kokiri and Poutama Trust.

Didymo triggered a biosecurity alert when it was first discovered in New Zealand in the Waiau River in Southland in 2004. Thought to be native to Canada, it is commonplace in parts of Asia and Europe and affects the diet of fish by reducing organisms they feed on.

A 2014 NIWA paper (National Institute of Water and Atmospheric Research) said didymo blooms, which to the touch feel like wet wool or fiberglass insulation, were of particular concern in New Zealand because it seemed that some of our most iconic and pristine rivers were at risk.

“The blooms look unsightly and are a nuisance,” the paper said. “They affect river users, interfering with angling, sporting and recreational activities and blocking water intakes.”

It is thought recreational users can spread didymo when it gets imbedded in the soles of boots, waders and field gear and for this reason groups such as Environment Canterbury highlight the importance of cleaning equipment.

The organisation’s regional lead – biosecurity, Graham Sullivan, said earlier this year that drying will kill didymo.

“Even slightly moist items can harbour didymo and other microscopic pests for months,” he said. “To ensure didymo cells are dead by drying, the item must be completely dry to the touch, inside and out, and left to dry for at least another 48 hours before use.”

The work by Williams in the South Island is one of eight river stories named as finalists by the Cawthron Institute.  The story category recognises those who are working at a regional level to improve the health of a river or rivers generally.