Lin­davia is a ‘clean wa­ter’ alga


Lake snot abounds. Is Wanaka’s wa­ter clean or dirty? Re­cently while chat­ting with peo­ple down at the lake I’ve be­come aware of an at­ti­tude that lake snot is thriv­ing in Lake Wanaka be­cause it is ex­pe­ri­enc­ing an in­crease in plant nu­tri­ents (ni­tro­gen and phos­pho­rus).

The op­po­site may be the case. Lin­davia is a ‘clean wa­ter’ alga but has flour­ished in its new home. It is an in­vis­i­ble sin­gle­celled di­atom that lives with other al­gae in a layer be­neath the sur­face. But when it mul­ti­plies, its sil­i­con walls latch onto neigh­bour­ing cells and clumps be­come vis­i­ble as lake snow.

In 2008, when I was help­ing a PhD stu­dent sam­ple wa­ter in

Roys Bay, we lo­cated the layer of lake snow and that’s ex­actly what it looked like – a snow storm.

Ac­cord­ing to Pro­fes­sor David Hamil­ton, New Zealand’s lead­ing lake ecol­o­gist, it is pos­si­ble that ex­plod­ing Lin­davia use up the mea­gre sup­plies of phos­pho­rus and ni­tro­gen in the wa­ter but must get rid of car­bon – by leak­ing it out.

The car­bon could be an en­ergy source for bac­te­ria that colonise the lake snow – con­vert­ing it into the much-loathed lake snot. And the lake snot is what has been block­ing fil­ters and coat­ing Lake Wanaka swim­mers, es­pe­cially this past sum­mer.

The com­bi­na­tion of Lin­davia cells, bac­te­ria and as­so­ci­ated mu­cus hangs in am­ber coloured strings in the wa­ter col­umn. Dur­ing the Ruby Swim one guy told me he thought it was his hair swirling in front of his eyes – but it turned out to be threads of lake snot. Swim­mers emerged with their faces cov­ered in an un­sightly film of these threads. I un­der­stand swim­mers who don’t shower im­me­di­ately be­gin to stink within an hour or so!

The mu­cus as­so­ci­ated with lake snot blocks fil­ters such as those in­stalled in town wa­ter sup­ply in­takes, wash­ing ma­chines, dish­wash­ers and gar­den sprin­klers. If not cleaned, the mu­cus sets like con­crete and the fil­ters must be re­placed.

ORC is re­search­ing Lin­davia’s ori­gins so we’ll know the kinds of lake con­di­tions it ‘‘nor­mally’’ in­hab­its and whether it morphs else­where into lake snot. And tap­ping into al­ter­na­tive town wa­ter sup­plies, such as Cardrona wa­ter, is a pos­si­bil­ity QLDC will no doubt be con­sid­er­ing.

As for a ‘magic’ cure? Like its river equiv­a­lent, Didymo (also a clean wa­ter di­atom), that’s un­likely. But sea­sonal and an­nual vari­a­tions in cli­mate and other fac­tors are likely to see lake snot come and go and some years it may cause no is­sues at all.

The fun­da­men­tal les­son though, with all or­gan­isms that are in­ad­ver­tently or oth­er­wise brought into our coun­try, is that our ecol­ogy is not adapted to these or­gan­isms and has no nat­u­ral de­fenses against their un­for­tu­nate im­pacts. And that is why biose­cu­rity is be­com­ing one of the fore­most is­sues fac­ing Aotearoa.

❚ Lau­rel Teirney is an aquatic sci­en­tist, fa­cil­i­ta­tor and writer.


Lau­rel Teirney

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