A campaign to replace old lifejackets with new ones has delighted Coastguard NZ.

The Old-4-New campaign saw over 3,000 lifejackets replaced over the summer, taking the campaigns four-year tally to over 10,000 being upgraded lifejackets.

Many of the lifejackets traded-in were unusable to the point of being dangerous.

Coastguard New Zealand spokesperson Georgie Smith says it's amazing to see the campaign so well supported.

"With drowning being one of the leading causes of preventable death in New Zealand, it's just great to get these old lifejackets out of boats and replaced with new ones."

The campaign found that some of the lifejackets on board had been purchased over 60 years ago.

Smith says a number were filled with Kapok that had become water laden, which is a great concern.

"They used to be a common sight decades ago, but now those lifejackets would be more of a hindrance than a help to people in an emergency situation."

More people died in preventable drownings in 2017 than 2016, with the number doubling to 22 deaths.