Otago Daily Times

Lake snow thought to have been re­duced by flood­ing

WANAKA

- KER­RIE WATERWORTH Ecology · Lake Tekapo

A FRESH­WA­TER sci­en­tist be­lieves heavy flood­ing last year could have helped re­duce al­gae lev­els in Lake Wanaka.

Chris Ar­buckle, who is also co­founder of Wanaka Lake Swim­mers and the Touch­stone project, is in­ves­ti­gat­ing where the weed, known as lake snow, has gone from around Ruby Is­land and ques­tion­ing when it will re­turn.

For the past three years, for six months from the end of Oc­to­ber and on ev­ery al­ter­nate Fri­day, Mr

Ar­buckle has taken pho­tos of the swim­mers be­fore and after their 2.5km swim around the is­land and mea­sured how much of the Lin­davia in­ter­me­dia di­atom had been caught on their skin.

For some rea­son, this year the wa­ters around Ruby Is­land have been much clearer.

He be­lieved it could be the re­sult of the heavy rains and floods last De­cem­ber.

‘‘The heavy rain put a lot of par­tic­u­late mat­ter into the lake, which seemed to have changed the preva­lence of the di­atom.

‘‘My hy­poth­e­sis or the­ory is that all that par­tic­u­late set­tled on the mu­cous and sunk it down to the bot­tom of the lake.

‘‘Un­for­tu­nately, it will still be there, but it is in­ter­est­ing that the water clar­ity has been a lot clearer than pre­vi­ously.’’

Swim­mer Krys­tle The­unis­sen has been in­volved in the project from the be­gin­ning and said the colour of the lake water after the De­cem­ber floods was un­like any­thing she had seen be­fore. ‘‘Al­most like Lake Tekapo.’’ For three years Mr Ar­buckle has also sam­pled the water from three sites around Ruby Is­land and mea­sured the clar­ity of the water at par­tic­u­lar depths.

He has posted the data on the Touch­stone web­site to pro­vide in­for­ma­tion on the lake’s water qual­ity and the pat­terns of lake snow in the part of the lake sur­round­ing Ruby Is­land and widen the un­der­stand­ing about the fu­ture water qual­ity chal­lenges fac­ing Lake Wanaka.

The Otago Re­gional Coun­cil con­trib­uted fund­ing to­wards the project but has also ap­proved the pur­chase of two new mon­i­tor­ing buoys for Lakes Wanaka and Wakatipu.

ORC sci­en­tist Hugo Borges said the two buoys were ex­pected to be built by Lim­no­track this year, but had been de­layed as Covid­19 re­stricted the com­pany’s abil­ity to carry out tests.

The buoys would be de­ployed in the lakes by June next year.

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