NIWA was reporting to Meridian Energy on algae and periphyton and fungal bacterial matter coating rocks and plants.
There was oxygen weed below Wairepo Arm near Twizel – a crossroad for dairy and salmon farms, Wells said.
Around the farms there was a lot of surface food and mats of periphyton – freshwater organisms attached or clinging to plants and other objects projecting above the bottom sediments.
The nutrient-fed growth was covering rocks and canal linings and stopping plant growth.
Below one Mackenzie salmon farm site, NIWA found tubificid worms normally at home in sewage treatment plants.
“It’s located under a particular (fish) farm that’s over-feeding.”
The resulting weed was clogging Meridian’s filter screens in the canals.
Wells knows which farms are involved and which are worse than others.
Soil monitoring could help scientists and regulators tackle nutrient overload but the work needs government funding, he said.
“I guess NIWA does the work but if you’ve got a government like the last one that wants the growth, to double economic growth, then you won’t get the research funding.”
NIWA has received some money from the state but nothing like it deserves, Wells said.
“Unless you put the money in you’re not going to get the answer.
“It’s pretty piecemeal to be honest.”
NIWA colleague and emeritus professor John Clayton, a specialist in aquatic biodiversity, said problems with lake and canal quality haven’t been addressed. While diving near salmon farms for weed research he and other NIWA staff had seen decomposing, uneaten fish pellets while swimming past farm tanks.
“Underneath the fish cages it’s not a pretty sight.”
Mt Cook Alpine Salmon chief executive David Coles, whose company is the major canal farmer, said “I’m not aware that weed growth is impeding generation flows and I’m sure our landlords would make us aware of any such impact.
“And no, we’re not over feeding and we are subject to annual, international audits under Best Aquaculture Practice who monitor these matters.”
The NZ-owned company harvests from canals operated by Meridian and Genesis Energy.
A Meridian spokeswoman said it actively manages the aquatic weeds in the canals through a weed eradication programme to ensure the power stations operate safely.
Environment Canterbury planned for and regulated discharges from the salmon farms and it was for the salmon farms to meet those obligations, she said.
Mackenzie high country farming leader and fine-wool grower Simon Williamson said salmon farmers should be subject to regular nutrient management monitoring, like livestock farmers.
Meridian was concerned but didn’t want to go public because of the risk environmental sanctions would hurt the local economy, he said.
Aquaculture, alongside farming and tourism, is a major employer in Mackenzie District.
Environment Canterbury upper Waitaki zone committee chairman Simon Cameron said salmon farming was one of several risks, including runoff from intensive farming, bird droppings and tourists pooing and peeing, to the region’s waterways. The difference between residual runoff and feeding fish high-protein ingredients was like smoking pot and mainlining, he said.
Water sports and other recreation were also a factor, Cameron said.
“It’s not salmon per se; it’s sport fishing and all these things which have brought these damn things (weeds) with it.”
Cameron, a sheep farmer, said Mt Cook Alpine Salmon was working on better feed efficiency to reduce waste.
The zone committee had pushed for it.
“We’ve asked for it and they’re on it now.”
It was good to debate salmon farming and other nutrient management issues openly, he said.
“There’s nothing like highlighting it to get people off their tails to do something about it.”
In 2013 NIWA announced the Waitaki weed surveillance plan – a partnership with Meridian and Land Information New Zealand to “routinely spray aquatic weed in the Ohau canals and Lake Benmore”. The weeds reduced native species habitat and “adversely impacts Meridian’s hydro generation operation”, NIWA said.
Reported problems with weeds included blocked cooling water filters and intake screens. NIWA agreed to work with meridian to monitor and manage plant growth and inform visitors, like rowers who descend on the Twizel area for regional and national championships. “This requires active surveillance inside and outside of the (pest plant) containment area, as well as the education of lake users in the area, especially for Lake Benmore and Lake Ruataniwha,” NIWA said.
