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Source: Close Up
A new menace, with fins and teeth and numbers on its side, is threatening New Zealand's waterways.
In Japan koi carp are treasured and you could pay up to $10,000 for one but in New Zealand they are a serious and voracious pest.
Koi carp have a big set of lips and after devouring their prey they spit out the leftover mud and help create an environmental catastrophe.
Lake Ohinewai in Waikato is teeming with carp and environmentalists have recently taken out 2.7 tonnes of pest fish, including goldfish and catfish.
Adam Daniel from the University of Waikato said there are about 70,000 pest fish in one lake alone and he said the biggest female they have seen had 700,000 eggs.
"One fish could repopulate the whole lake," Daniel told TV ONE's Close Up tonight.
The carp leave deep holes from foraging for prey and that's the big killer, Daniel said. "He's a big mud pump. Continually pumps mud back in and dirties the lake."
At certain times of year the process causes more algal bloom and less sunlight gets through.
Daniel said this has seen the plants go, along with the ducks, most native fish and shellfish.
The problem is compounded by intensive farming and in the Waikato the combination of pest fish and nutrient load from farming has made the situation twice as bad.
John Gumbley from the Department of Conservation said dozens of lakes in the Waikato region are in very poor condition. "None of these lakes you can drink from, none safe for stock to drink from."
Daniel said it is hard to support Prime Minister John Key's remarks that in comparison with the rest of world we are 100% pure.
"If you look at all the lakes between Auckland and Hamilton it's really, really bad," he said.
Lakes in countries like Norway and Sweden are known to be much cleaner than in the Waikato.
"The water quality I've seen here is similar to some third world countries I've visited," Daniel said. "I hadn't seen stock in streams before I visited New Zealand.
But in the Waikato they are taking steps to redress the balance through easily managed small traps and more complex commercial ones which can net about 350 kilos in one catch. The fish that are caught get minced up for pet food and are also turned into fertiliser.
The nets are designed to catch the carp when they travel in canals between lakes and rivers. And buffer zones have been set up with native plants to keep out livestock.
"We might get the lakes coming back in at best 30 years..it's a long haul but I think it's worth it," said Daniel.
Waikato University Professor David Hamilton said a lot more sustained action is needed to reverse the major decline in the water quality of our lowland lakes.
He told Close Up the lowland systems are being impacted by multiple land use, pest fish and weeds.
Hamilton is the president of the New Zealand Freshwater Sciences Society and said the lakes are "degraded to severely degraded right throughout New Zealand".
Lakes are a feature of the coastal environment of New Zealand, Hamilton said, adding that they are suffering from intensifying agriculture in their catchments.
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