Coun­cils must act on wa­ter qual­ity

Central Otago Mirror - - CONVERSATIONS - DON ROBERT­SON

It’s good to see Ed Tay­lor rais­ing the issue of Lake Wanaka wa­ter qual­ity in the July 13 Mir­ror.

Things seem to be chang­ing in Lake Wanaka. Each year there are more con­cerns ex­pressed by fish­er­men about lake snow (or lake snot) clog­ging fish­ing lines and im­pact­ing fish­ing suc­cess.

Fil­ters in boat cool­ing sys­tems be­come blocked, and both com­mer­cial and do­mes­tic users of town sup­ply wa­ter are ex­press­ing con­cern about fil­ters clog­ging more fre­quently.

In early June this year a large al­gal bloom about 6 hectares in size was seen in Steven­sons Arm. When wa­ter was sam­pled there in mid June, even after a strong northerly, there were high num­bers of the di­atom (a kind of plank­tonic al­gae) associated with lake snot present. Such large al­gal blooms are nor­mally associated with nu­tri­ent avail­abil­ity.

Our pris­tine deepwater alpine lakes are at risk. Coun­cils do not ap­pear to have the re­sources to meet their statu­tory re­spon­si­bil­i­ties for lake wa­ter qual­ity man­age­ment or the catch­ments feed­ing into them.

Our alpine lakes have been re­cip­i­ents of build-up of mul­ti­ple decades of ur­ban, agri­cul­tural and recre­ational run-off of nu­tri­ents, tox­ins, pathogens, par­a­sites, and decades of build-up of in­va­sive aquatic plants and an­i­mals.

The Guardians of Lakes Wanaka and Hawea are con­cerned that the risks faced by the lakes are not be­ing man­aged. Ed Tay­lor men­tioned a mon­i­tor­ing buoy for Lake Wanaka. The Guardians place pri­or­ity on the de­vel­op­ment of a lakes man­age­ment plan which in­cor­po­rates and builds on the val­ues and wishes of lo­cal com­mu­ni­ties. Such a doc­u­ment would then pro­vide a frame­work for the plan­ning of ap­pro­pri­ate re­search and mon­i­tor­ing lead­ing to ef­fec­tive man­age­ment ac­tions.

Our deepwater lakes are com­plex ecosys­tems and while mul­ti­ple mon­i­tor­ing buoys will be a part of the solution in wa­ter less than 80 me­tres deep, most (around 85%) of Lakes Wanaka, Hawea and Wakatipu are much deeper than that. Pre­vent­ing the de­cline of wa­ter qual­ity and pro­tect­ing our alpine lakes ecosys­tems is vi­tal for the on­go­ing vi­a­bil­ity of the com­mu­ni­ties that de­pend on these lakes con­tin­u­ing to at­tract peo­ple to the re­gion.

Re­duc­ing the risks of in­creas­ing nu­tri­ents, of in­creas­ing pol­lu­tants and spread of in­va­sive species will re­quire much greater in­vest­ment by coun­cils, busi­nesses de­pend­ing on (or im­pact­ing) lakes wa­ter qual­ity, and com­mu­nity groups.

There are also roles for the Min­istry for the En­vi­ron­ment and Depart­ment of Con­ser­va­tion. The cur­rent level of ac­tiv­ity by Otago Re­gional Coun­cil and

Queen­stown Lakes District Coun­cil will re­sult in the lakes con­tin­u­ing to face in­creas­ing risk of de­clin­ing wa­ter qual­ity.

Dr Don Robert­son is re­tired. He has 38 years of ex­pe­ri­ence in aquatic re­source man­age­ment and re­search. He is also in­volved with the Guardians of Lake Hawea.

Don Robert­son was chief sci­en­tist for bio­di­ver­sity and biose­cu­rity for NIWA.

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