Two serious boat crashes have sparked a warning for boaties to be ultra-vigilant when towing thrill-seekers.
A 36-year-old Rotorua man died and another man was injured after two boats collided on Lake Ohakuri, southwest of Rotorua, about 4.15pm on Monday.
The incident came just two hours after five people, one a small child, were injured when two boats collided on Lake Middleton in Otago.
Both incidents involved boats towing sea biscuits - inflatable rings on which passengers lie.
Water Safety chief executive Matt Claridge said boaties needed to know the traffic rules so they were always in the best place at the right time.
"It's pretty difficult when you're towing someone behind the boat because you're looking forward, you're looking back.
"On the lake you can obviously drive in any direction you like, so you can get blindsided very easily. And when there's a lot of boats, obviously the likelihood of that occurring is far greater."
Ultimate responsibility lay with the skippers. "They need to be ultra-vigilant and they need at least one, probably two people on lookout, watching not only the skier but for other boats," he said.
People being towed behind boats could also play a part by making themselves visible. "So whatever you've got - if you've got skis, a toboggan, a biscuit - you need to use that wherever possible as a means to identify yourself to any boats travelling towards you. Because often with the glare of the water, you can't be seen."
Police are still piecing together the circumstances behind the collision in which the man died.