Con­tam­i­nated lake’s de­cline alarms

Nelson Mail - - FRONT PAGE - NINA HINDMARSH 6 Opin­ion 8 Weather & TV 10 Cat­a­lyst 12 Puz­zles

A Golden Bay lake has be­come an unswimmable, con­tam­i­nated mess and res­i­dents say stormwa­ter runoff from a dairy farm and hous­ing is to blame.

For the past two sum­mers sig­nif­i­cant al­gal bloom, or cyanobac­te­ria, has been in­creas­ing in Lake Kil­lar­ney, nes­tled in a re­serve be­hind Com­mer­cial St near the town’s centre.

Since 2004 stormwa­ter from neigh­bour­ing farm­land and res­i­den­tial prop­er­ties has been di­verted into the lake.

Res­i­dent Dave Kennedy said the lake was ‘‘clear blue’’ when he first shifted there 30 years ago, but th­ese days it was of­ten a ‘‘murky­brown’’.

‘‘I think it’s only since they di­rected the stormwa­ter into lake that it’s started caus­ing the harm,’’ he said. ‘‘Our kids used to swim in it, but you wouldn’t like to now.’’

While sed­i­ment anal­y­sis is due in Oc­to­ber, Tas­man District Coun­cil re­sults to date re­veal a ‘‘sig­nif­i­cant’’ nu­tri­ent and or­ganic con­tam­i­na­tion.

Neigh­bour­ing Takaka res­i­dents are in­creas­ingly con­cerned about the dis­coloura­tion and po­ten­tial ef­fects of the al­gal bloom on ad­join­ing prop­er­ties.

John Lewis said the lake was still very blue when he moved there five years ago, but in the last few years he had no­ticed the dis­coloura­tion in­crease dur­ing the sum­mer months and after rain events. ‘‘You wouldn’t like to stick your toes in there now,’’ he said.

Lewis is tak­ing reg­u­lar wa­ter sam­ples and pho­to­graphs for the coun­cil, whose engi­neers are try­ing to solve the prob­lem.

He said the con­tam­i­na­tion was com­ing from the coun­cil-owned pipe, which was drain­ing from a sump on the ad­ja­cent dairy farm pre­vi­ously owned by Fon­terra, and into the lake.

Al­gal blooms are typ­i­cally the re­sult of a buildup of nu­tri­ents and need warmth to grow. An­other po­ten­tial source was from the leaves of de­cid­u­ous trees, he said.

Dur­ing heavy rain sev­eral weeks ago, his wife Anne Lewis said she no­ticed wa­ter com­ing out of the drain was ‘‘the colour of mud’’.

‘‘You could see the dis­coloura­tion spread­ing through the whole lake. The area of dis­coloura­tion got big­ger and big­ger un­til it cov­ered the whole lake.’’

The lake is home to the rare dabchick duck. Anne Lewis said there was a ‘‘marked re­duc­tion’’ in the num­ber of duck­lings in the lake last spring, but wasn’t sure if this was be­cause of the con­tam­i­na­tion, or a snap­ping tur­tle that had taken up res­i­dence.

A re­port by TDC en­vi­ron­ment and plan­ning man­ager Den­nis Bush-King said the pipe to the lake was orig­i­nally in­stalled in 1970.

How­ever, only since 2004 had flood­wa­ters from farm­land and res­i­den­tial prop­er­ties on Mei­hana Street been ac­cepted into the sys­tem. ‘‘It ap­pears that th­ese over­flow events to the lake are com­mon even in rel­a­tively small rain­fall events when soils are sat­u­rated,’’ he wrote.

‘‘Re­sults from sam­ples of this stormwa­ter are pend­ing, and dis­cus­sions about pos­si­ble di­ver­sion of this stormwa­ter have be­gun in­ter­nally.’’

Dis­solved oxy­gen pro­files and sed­i­ment sam­ples were col­lected in July. Oxy­gen was fully de­pleted in the lower few me­ters of the lake.

TDC spokesman Chris Choat said it had ap­plied for En­vi­rolink fund­ing to get ad­vice on de­vel­op­ing a more com­pre­hen­sive plan ‘‘to in­form us as to the sit­u­a­tion and re­me­dial op­tions. ‘‘It’s not toxic at this stage, but we would ad­vise people to avoid con­tact with the wa­ter,’’ he said.

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