The experience of swimming with dolphins and watching the animals in their natural habitat is so popular that it generated NZ$24m (£8.7 million) for the New Zealand economy last year, according to reports.
Ministry of tourism figures sourced by the New Zealand World Wildlife Fund (WWF) showed that around 103,000 people took part in dolphin watching or swimming last year.
The WWF has been pursuing a campaign to protect Hector’s dolphins, the species that the south island tourism industry focuses on, and Maui’s dolphins.
Chris Howe, executive director of the WWF New Zealand, said: "Obviously, Hector’s dolphins are in fact priceless.
"They are amazing creatures and live only in New Zealand. But their economic value is another reason to protect them."
New Zealand has enjoyed rising popularity as a tourist destination in recent years, with many travellers heading there to see its dramatic landscapes. It is also popular with fans of adventure holidays and offers activities such as sky diving, hot air ballooning, caving and snowboarding.