How to dig a hole in a lake: Drone captures opening of Te Waihora/Lake Ellesmere
Opening Canterbury's largest lake is no mean feat, as revealed in new drone footage.
Heavy machines have parted nearly 300 metres of material to connect Te Waihora/Lake Ellesmere to the sea, allowing fish to migrate back into the lake.
Environment Canterbury's (ECan) aerial footage shows the machines being buffeted by waves as they work on the beach.
The lake has been regularly opened since at least the early 1800s, before European settlement. More than 300 openings have been recorded.
The openings are a collaboration between ECan and Ngai Tahu.
The latest opening took five days, relatively quick due to favourable weather. In rough conditions it could take six weeks to open.
"During this opening the sea was relatively calm; you can imagine the risks when the waves are a little bigger," ECan river engineering manager Leigh Griffiths said.
"It's dangerous work and we are fortunate that our staff and contractors are so experienced."
During rough seas, waves can crash over the beach and into the lake itself.
The current opening is about 290 metres long, with 30,000 cubic metres of material removed.
Openings are closed naturally by gravel washing from the sea and closing the passage.
If lake levels remained low and seas were calm, it may have to be artificially closed.
The lake openings are also used to minimise the risk of flooding.