A clear message to boaties from police: be properly prepared or risk facing prosecution.

Queenstown Police are reminding those heading out on the water this winter that the weather can change in an instant.

They say a number of water rescues occur because of people that go out ill prepared, and it's a waste of police resources.

It follows the rescue of two people Friday night who were caught out on Lake Wakatipu in an inflatable boat with only one lifejacket.

The boat had no motor and the pair were left with only one oar after the other broke.

Police said they spent considerable time getting the pair safely back to shore in a situation that could have easily been avoided.

Police, Maritime New Zealand and local authorities all have the power to take enforcement action against those acting irresponsibly on the water and said they won't hesitate to do so.