Drone footage has captured the full impact of the recent floods on the ecosystem in Canterbury – and experts say it'll be felt for months.
Maitu Prebble of the local Wairewa Rūnanga said "potentially hundreds, if not a thousand or more" tonnes of sediment had washed down into Wairewa/Lake Forsyth.
Drone footage taken by 1News showed the waters around 45km south of Christchurch had been inundated, transformed from its normal deep blue to a muddy brown.
At the point where the lake opened to the sea, the murk was spilling into the coastline, leaving a long stain along the water.
Drone footage reveals full impact of Canterbury's widespread flooding - Watch on TVNZ+
"That's the colour of the clays that are coming from that surrounding landscape," Prebble explained.
The material had been washed down from various rivers into the catchment and also fed from surrounding hill country and cliffsides.
The country there in Banks Peninsula is capped by a type of wind-blown silt called loess, which is vulnerable to erosion and easily brought down by rain.
It was already smothering aquatic plants, originally put in to improve the quality of the lake.
"There will be no light penetrating the water’s surface, so being photosynthetic plants, they'll be suffering under these conditions and probably dying back."
Wairewa has the highest density of eels of any catchment in New Zealand – but their outlook was also uncertain.
Many were likely to have gone out to sea when the lake was opened following the flooding, Prebble said.
"It does mean that the eel fishery is pretty vulnerable for this season."
Environment Canterbury is also taking samples after nutrients were washed down from the soil in surrounding land.
There would be "no quick fix" at the lake, ECan's water and land science manager Elaine Moriarty said.
"Every time we get some wind, we suspend [those nutrients], and slowly you get a release of nitrogen and phosphorus coming out of the lake, and that then can lead to long term problems like toxic algae bloom."
Toxic algae can be dangerous for any animals and humans in the area, and conditions will be monitored closely by the rūnanga and ECan over the coming months.
That’s a challenge the custodians there say they’re ready to face.
"It's embedded and inherent in the name of the lake, which is called Wairewa, which means water's rising rapidly," Prebble said.
"We know from the past that this ecosystem here changes massively, but what we do also know is that our people for our time have adapted to those changes."
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