An area of ocean off Taranaki roughly 50 times the size of Lake Taupo will be turned into a marine mammal sanctuary by the Green Party.
It'd be the largest sanctuary in the country, covering a major feeding ground for blue whales and 36 other mammals.
It's also an area subject to a recent seabed mining grant, and is in constant threat of oil drilling by prospective offshore companies.
Greens leader James Shaw said seabed mining is devastating for marine life.
"For blue whales this is a bit like having the contents of a vacuum cleaner dumped onto your dinner plate. And, so it is hugely disruptive to their feeding patterns."
He said the Greens will protect the species instead of allowing seabed mining and oil drilling where they feed.