Fears lake snow could make Lake Wakatipu 'unfishable'

Thursday, 1 September 2016

An experienced fishing guide fears Lake Wakatipu could end up 'unfishable' with the invasive spread of the algae bloom, lake snow, and warns Lake Dunstan could be next.

Queenstown fishing guide Stu Dever, armed with his rod and reel, voiced his concerns about the presence of lake snow in Lake Wakatipu to Otago Fish and Game committee members at a meeting in Cromwell last month.

His rod was clogged with the thick globules of algae after only one day's fishing on the lake.

'That rod, I only used once for one fishing trip and got that build-up from lake snow - the problem is very bad. It has got to the stage if you don't clean your reel you can't wind it in it gets that thick.'

The mucous-like substance is produced by the algae cyclotella has now been observed in three South Island lakes.

In May, slime taken from Lake Wakatipu was confirmed as lake snow. The algae was also found on a fishing line at Lake Coleridge in 2015, after initially being discovered in Lake Wanaka in 2004.

Dever said he first noticed the thick globules of algae in Lake Wakatipu in April and it had got progressively got worse. 

'It is on the top but it's also down deep and right through various levels. I have no idea how it got into the lake but I if nothing is done about it, I don't no where it could end up. The lake could be totally unfishable. How bad is it going to get? It has just started now and it's bad enough.'

He warned the spread would flow-on to Lake Dunstan, in Cromwell.

'It will flow on to Lake Dunstan - our lake drains into Cromwell from the Kawarau River…Something has to be done now, urgently.'

Aside from the inconvenience, the algae was not a good look to overseas anglers.

'They say to me, 'what is this?' They can't believe it.'

'The algae also blocks boat filters and I understand our drinking water comes out of the lake and the algae is blocking the filters for the town's water supplies. That is one of the major things for Wanaka, it gets into the irrigation pumps.' 

Otago Fish and Game operations manager Ian Hadland said lake snow was not a new issue with lake-users struggling with it in Wanaka, but it had not been prevalent in Lake Wakatipu up until this point.

'It is a relatively new phenomenon there and it is the worst we have seen it at both.'

It had not been noticed in Lake Dunstan but the Cromwell lake was at risk, he said.

'We don't know much about it….There is a lack of science in the area and we need to catch up on that really quickly to stay on top of what's going on.'

There were suggestions it could be naturally occurring through climate change or it could be related to land use, he said.

There was a fear greater land intensification around the outer regions could be responsible for introducing nutrients in the water. 

'Usually algae bloom are responsive to changes in nutrients. It is a real concern because Queenstown is a place that relies heavily on a clean, natural environment. Clean water is one of those things people around the world really appreciate. They can't believe the clarity of the deep, blue lakes.

'Rotorua lakes got to the point the got really green and that's not the sort of thing you want to see down here. It drove people away - particularly anglers.' 

An Otago University academic had been researching the algae bloom, he said.

'They have been pretty concerned about it and about changes happening to the lakes we are only becoming aware of.'

Fish and Game intended to liaise with the Otago Regional Council to see what monitoring it had in place, what it proposed to do about it, and try to understand how it got there, he said.