The owner of a sailing school says it's very unusual to have three yachts capsize in one regatta.
It happened yesterday afternoon when strong winds replaced calm conditions at the start of a race on Lake Aviemore in North Otago, causing the yachts to overturn.
Police were notified and attended the scene, along with the coastguard and ambulance service.
Seventeen people who were in the water had to wait up to 20 minutes to be rescued, and nine had to be treated for hypothermia.
An experienced Auckland sailing instructor, Penny Whiting, said winds at this time of year could make sailing challenging.
"It sounds horrific - three boats and 17 people in the water, but of course sailing in that particular region, it's really like the wind funnels around the place and it would be quite frisky sailing in spring."