A structure which resembles a mussel farm has appeared on Lake Hayes this week, but those thinking that shellfish are being cultivated in the lake could not be more mistaken.
Two Niwa scientists, Dr Christopher Hickey and Max Gibbs, of Hamilton, installed the structure this week, hoping to understand the causes of the algal bloom in the lake and what can be used to treat it.
Ironically, Lake Hayes is the cleanest it has been for years, they said.
Dr Hickey said the "lake tubes" - 10m long bags - had been erected 50m out from the shore of the lake and extend to the lake floor.
The bags are joined together and weighted at the bottom ensuring the sediment of the lake was captured and "capped".
"We've done it to try and understand how much phosphate comes out of the bottom of the lake," Dr Hickey said.
"That's what drives the algal blooms in this lake.
"We can then try a number of different treatments.
"We've got a range of different products, like allophane clay and zeolite clay."
During the research, the water in the tubes would go anoxic - where the oxygen was removed - which would release the phosphate and ammonia in the lake, allowing algae to grow.
In summer, Lake Hayes had a tendency to become stratospheric, which allowed the algae to move up and down through the layers of the water getting its nutrients.
By trying several different treatments in the lake tubes, the scientists would see which treatments were most effective, and use the results of their research to develop models for restoring water quality in other lakes in New Zealand.
"If you're going to commit to this sort of process, you have to spend quite a bit of money and you have to know it's going to last a long time," Dr Hickey said.
"The approximate quantity of sediment-capping material needed for Lake Hayes ranges from 250 tonnes of alum to 550 tonnes of modified zeolite, with indicative material costs of $125,000 to $1.4 million."
The application costs would be added to that amount, with the "optimal capping blend of materials and quantity" to be determined by the trial, he said.
It was the first large-scale testing of its kind in New Zealand.
Although they knew it worked in the laboratory, "proving it on a greater than laboratory scale" was the goal, Dr Hickey said.
"The experiment will run for about a month.
"There are 15 tubes out there [including control tubes].
"It's a Niwa project and part of the programme is looking at the restoration of lakes and other bodies, like rivers and streams.
"This will be used to compare to the results on another lake in the North Island."
Dr Hickey said testing was also being done on Lake Rotoiti - a soft-water lake with "blue-green algae".
Lake Hayes was a hard-water lake with "orange-brown algae".
However, the algae which has plagued the lake over previous summers, was surprisingly absent this year, due to an abundance of Daphnia, also known as "water fleas", he said.
"At the moment, the lake is as clear as it's ever been.
"There's a 10m drop where we put the tubes in and you can look right down to the bottom.
"When we planned this experiment we expected 3m visibility.
"The reason is the Daphnia."
Dr Hickey said the plankton, which range in size from 2mm to 5mm have managed to regenerate and are grazing on the algae, which has helped to restore the lake.
