Transpower has detailed the thousands of dollars worth of fines dished out for fishing near the Cook Strait power cables.
Three power cables run for 40 kilometres across Cook Strait between Oteranga Bay near Wellington and Fighting Bay in Marlborough.
Five telecommunications cables also run across the waterway.
The first cables were originally laid in 1965, making them one of the first submarine cable links in the world.
Replacement cables were laid in 1991 and are due to be replaced again in 2032.
They can transfer up to 15 percent of New Zealand's power between the two islands.
The Cook Strait protection zone runs along the length of the cables, is seven kilometres wide and patrolled 24/7 by boat. It prohibits fishing of any type or anchoring.
The Cook Strait power cables area is patrolled by boat 24/7. Photo: Supplied / Transpower
Since 2006 there had been about 21 fines dished out for fishing in the area, Transpower executive general manager grid delivery Mark Ryall told RNZ.
They included a recreational fisherman who had received multiple warnings, a charter boat which was positioned in the cable zone whilst knowing it was illegal and a person in 2010 who laid cray pots in the zone.
"Obviously something like that getting dragged across the cables could do damage."
Fines had ranged from $1000 to $20,000 but generally Transpower would take the approach of educating people in the first instance, Ryall said.
Prior to the Cook Strait cable zone being established in 1996, there had been five instances where the cables had to be repaired.
Fishing is prohibited near the Cook Strait power cables. Photo: Supplied / Transpower
Ryall said the cables were inspected every year, and modelling showed the likelihood of them failing increasing in the 2030s.
That triggered a plan to replace them in the next decade.
"The international offshore cable market is exceptionally busy, and you are looking at lead times in the ballpark of seven years so we've actually got that project already underway."
Ryall said replacing a cable was a significant exercise, so it emphasised the need to protect the current one whilst it was operating.
The maximum fines for fishing or anchoring in the Cook Strait cable zone is $100,000, while the maximum fine for damaging the cable zone is $250,000.
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