Ashburton District Council chief executive Hamish Riach has defended the decision to close Lake Hood.
The council closed Lake Hood to the public on April 3 because of the risk to public health from the cyanobacteria algae present in some areas of the water body.
“The decision was made to close Lake Hood based on advice provided and because of the genuine health risk,” Riach said.
Riach said the council was “following advice to treat the whole aquatic area as one water body”.
“We have previously discussed splitting the lake into sections to limit any public health warning to specific areas.
“However, the advice we received from external bodies, including Health New Zealand and ECan, is that the lake should be treated as one water body given the circulation and dynamic nature of water bodies.
“For this reason, Health New Zealand issue the public health warning for the entire lake, not sections of the lake.”
The council's decision to close the lake came after two people were poisoned by the toxic algae.
Both incidents occurred before the health warning was imposed on March 20 by Health NZ - which has not disclosed where in the lake the people came into contact with the algae.
Water Ski Lake Hood was stunned by the decision to close the entire lake two week’s out from hosting the sport's national championships on April 15-21.
Club secretary Janeen Donaldson said the club felt there was no justification to close the whole lake and is devastated by the decision.
She said the recent testing showed algal blooms were in small areas and around the canals, over a kilometre away from the ski lane.
She said it was frustrating when the water in the ski lane is clear and there seemed to be "no justification for it”.
Earlier in the season there had been some signs of algae buildup around the ski area but that was washed away when the council contractors dug a new channel at the end of the water ski lane to improve water circulation.
Testing results provided to her from the council showed the ski lane hasn’t been tested for potential algal blooms since mid-February, she said.
The club has requested the council review the closure decision, asking for further water testing on the ski lane and in the body of the main lake to show there is no risk Donaldson said.
Riach has ruled that out “based on current information”.
“The monitoring procedure requires two clear consecutive weekly test results before the health warning can be lifted.”
Ecan’s Lake Hood monitoring involves a visual inspection at six locations -including the ski lane -around the lake for algal blooms and when one is spotted, a sample is taken to identify the algae she said.
“The national guidelines are you take a sample from the worst-case scenario for molecular analysis”.
The recurring tests are at the same location each week until the lake is cleared of the bloom she said.
She said while the algae may be found in a certain area of the lake, the health warning covers the whole lake.
Moriarty added the toxic algae is dynamic and not stationary like a plant so it can drift around with the currents in the lake.
- LDR is local body journalism co-funded by RNZ and NZ On Air.
