The Mysterious Case of the Slimy Algae: what we know – and don’t – about the ‘Lake Snot’ invading Queenstown lakes

November 23, 2016

The invasive didymo and more recent lake snot recently found in Lake Wakatipu share characteristics – but there is one difference that makes lake snot more problematic, University of Otago freshwater scientist, Dr Marc Schallenberg says.

Both are diatoms (a type of algae) with long polysaccharide threads made of chiton that they secrete. Didymo’s tail is cotton-like and not sticky. With lake snot, the threads form a sticky slime of greater nuisance value – clogging water filters and sticking onto swimmers, fishing gear and boats – that could potentially be less susceptible to chemical control, protected from treatment agents by its cover of slime.

Lake snot is not common, but has been found in some lakes overseas in Europe, America and Israel. Wanaka fishermen reported a slimy presence in 2004, scientists identified what it was when they found it in their nets in 2008. It spread to Lake Wakatipu and Lake Hawea this year. In Lakes Hayes and Aviemore, the diatom had been reported in the early 2000s, but there were no reports of lake snot. Examination of old samples and reports suggest that the same lake snot appeared in lakes Benmore and Waikaremoana, but subsequently cleared up. No one knows why.

In fact, says Marc, very little is known about it. Studies of Lake Wanaka lake bed cores did not detect the lake snot-producing diatom before the early 2000s. Genetic work showed that the lake snot diatom in our lakes is Lindavia intermedia, which is genetically very similar to a North American strain of this alga. However, this doesn’t guarantee that our nuisance diatom is a recent invader because some algae are naturally cosmopolitan.

Problems start occurring when Lindavia forms into macro-aggregates, a big bunch of Lindavia and other lake organisms stuck together by the slime. Two key parameters govern whether this happens – the stickiness of the slime and the frequency of collision between microscopic algae and other particles. The more often they bang into each other and the stickier they are, the greater the problem. The chemical properties of the slime and reasons for its production are still unknown.

At this point, the scientists only have hypotheses as to how lake snot could affect the ecology of our lakes. Our lakes are so clear because they are low in nutrients (nitrogen and phosphorus). In such lakes, the food chains between algae and fish tend to be very long. Lake snot’s macro-aggregates probably shorten the food chain between algae and fish. Scientists’ hypotheses on lake snot’s specific effects on lake water quality, turbidity and fish populations are as yet untested.

Marc says there has been little research into lake snot in New Zealand and elsewhere and until recently, there has been little interest from local authorities or others to fund what he believes are important investigations into understanding the causes, implications and possible solutions to this threat to our lakes.

But a research proposal is soon to go into MBIE and discussions have begun with Otago Regional Council. Public support for both would be welcome, he adds. Letters can be sent to him at