Rare ‘lake snot’ mysteriously spreading through South Island lakes
It has been compared to didymo, the nuisance algae which has plagued rivers around the country over the last decade.
“Lake snot” – a mucous-like substance produced by the algae cyclotella and known overseas as “lake snow” – has been observed in three South Island lakes.
It made its way into Wanaka’s public water supply, clogging filters on household appliances and preventing people from fishing in the lake.
The slime is tasteless and poses no risk to human health.
It has puzzled scientists, who are yet to find an explanation for why the lake snot originally formed and how it had spread to otherwise healthy lakes.
University of Otago scientist Dr Marc Schallenberg has been studying the algae since 2008, and said it caused problems for residents.
He and a team of scientists from Landcare Research and Canada’s Université Laval were hoping to research the effects of lake snot and why it had suddenly appeared in more South Island lakes.
“We were scratching our heads as to why this problem should suddenly appear in these relatively unpolluted lakes,” he said.
“There was an obvious similarity to the invasion of relatively unpolluted South Island rivers by the nuisance algae, didymosphenia geminata [didymo] in around 2004.”
It has caused problems for fishing operators, who found the slime attached to their lines.
There were reports earlier this year of swimmers at a multi-sport event emerging from Lake Wanaka with lake snot hanging off them, Schallenberg said
It had trialled a new water treatment system which would remove the algae from the supply.
“When this unpleasant material stops you fishing, sticks to you when you’re swimming and clogs the water filters on your washing machine, dishwasher and sprinkler, you get the picture pretty quickly,” Schallenberg said.
The scientists had several hypotheses regarding the emergence of the lake snot. Climate change and agricultural intensification were possible factors.
Further research had been stymied by a lack of funding, Schallenberg said.
“I’m not sure if this reflects the general low levels of investment in science in New Zealand or that there is a reticence by governments to support research into emerging environmental problems for fear that our reputation as ‘clean-green’ country will be tarnished.
“The local people understand the importance of cyclotella and lake snot, not just to them and their lake, but to the bigger picture of New Zealand’s changing environment.”
What can be done to stop lake snot?
It’s like something you might encounter in a nightmare.
You’re swimming fish-like through the crystal-clear waters of a deep lake. Suddenly you notice that the clear blue water contains bits of almost clear mucous floating in it. As you swim on, the mucous starts sticking to you and then you’re covered in a thin coating of slime before you start panicking and wake up from your dream in a cold sweat.
Starting around 2004, people fishing in Lake Wanaka began noticing an unusual slime sticking to their fishing lines and lures – something they’d never seen before. In 2008, the University of Otago lakes research team identified the newly observed, almost transparent, mucous particles in Lake Wanaka’s water as a rare phenomenon called “lake snow” and they linked it to the presence of a new algae found in the lake waters called Cyclotella bodanica (recently renamed by algologists as Lindavia intermedia).
It also seemed likely to the team that the increasing reports of clogged domestic water filters in Wanaka township were linked to this new occurrence of lake snow and Cyclotella.
While lake snow is a rare phenomenon, marine snow is more common and gets its name from the almost transparent or whitish mucous flocs typically seen in many ocean environments. However, the slimy flocs now floating on some of our lakes, fouling our fishing lines and clogging our filters looks more like lake “snot” than lake “snow”.
Thanks to reports from fishermen and boaties, we know that lake snot subsequently turned up in Lake Coleridge around 2012. In April this year it was discovered in Lake Wakatipu by a local fisherman. The research team’s collaborator, algae specialist Dr Phil Novis from Landcare Research, has confirmed that the same species of algae is associated with lake snot in all three lakes.
The spread of lake snot through our big and relatively pristine alpine lakes has obvious economic implications in terms of domestic and industrial water supplies, recreation and tourism. However, lake snot also raises many scientific questions related to the potential roles of biological invasions and environmental change.
While Cyclotella bodanica had been recorded in other South Island lakes prior to the southern lake-snot problem, our work on sediment cores carried out with Canadian collaborator, Dr Emilie Saulnier-Talbot from Laval University, showed that Cyclotella bodanica had not proliferated in Lakes Wanaka and Wakatipu prior to the problem developing in the other lakes. This suggests while the recent problem in the southern lakes could be related to a biological invasion from other lakes, recent environmental changes that have been occurring in the lakes probably also plays a role.
As with its river cousin Didymosphenia geminata (didymo), the nuisance factor of Cyclotella is not that it reaches high-cell densities in the lakes but that it secretes a lot of slime, a carbohydrate polysaccharide produced by the cell.
In the case of didymo, the purpose of the polysaccharide is clear – a long polysaccharide stalk connects the didymo cells to the rocks on which they grow. Dense growths of the stalks cause the typical mat-like appearance of didymo in rivers in which it blooms. In the case of lake snot and marine snow, the purpose of the sticky polysaccharide secretions remains the source of much scientific speculation, requiring further investigation.
The secretion of sticky mucous causes aggregation of cells and other particles suspended in the water into flocs and strands which are large enough to be seen by the naked eye and to clog water filters. One hypothesis is that such aggregation could reduce grazing on the algae by filter-feeding organisms or that it could slow down the sinking of the algae into the poorly lit bottom waters and ultimately to the sediments, where they die.
Another more controversial hypothesis is that the overproduction of polysaccharide by algae occurs as a response to nutrient starvation in conditions where temperature and light are sufficient for growth and reproduction.
Under these conditions, it could be advantageous for the algae to maintain photosynthesis and carbohydrate production so that the phytosynthetic machinery is primed for when scarce nutrients such as nitrogen and/or phosphorus become available. However, experiments that our team conducted with algae from Lake Wanaka showed lake-snot production was stimulated by adding nitrogen and phosphorus, a result that is inconsistent with the nutrient-starvation hypothesis. So, further research is required to pinpoint why this Cyclotella species secretes such large amounts of mucous.
The South Island high country is undergoing many transformations, including agricultural intensification, urban development, increasing tourism pressures and climate change. Lakes are also affected by invasive species which can be spread by the increasing recreational activities that our beautiful lakes afford.
Given these pressures on the environment, the monitoring of the health of our aquatic ecosystems has been inadequate and under-resourced. We have had little success attracting research funding from any level of government to study and answer questions on lake snot.
In contrast, our discussions with the people of Wanaka show they understand the importance of Cyclotella and lake snot, not just to them and their lake, but to the bigger picture of our changing environment. A short video has been produced about lake snot in Lake Wanaka: https://vimeo.com/15243706
Dr Marc Schallenberg is a member of the lakes research group in the department of zoology at the University of Otago.