There's now no escape from the speed limit, even on the water. Maritime officers are trialling water laser speed guns to catch speeding boaties in Marlborough - and other councils are interested.
The officers and Marlborough District Council Harbourmaster's staff have been on the water catching out those breaking the law.
Maritime NZ acting director, Nigel Clifford, says speeders will get infringement notices - which come with a fine of $200 each.
In a two-hour trial last week 10 recreational boaties were caught speeding.
"Compliance with speed rules was not great," says Marlborough Harbourmaster Luke Grogan.
"We get lots of emails and phone calls complaining about boaties speeding close to shore and in busy areas.
"Speeders are unhappy when we catch them but their speed puts children, swimmers, divers and other boats at risk."
Nationwide, the five knot rule is in place within 200 metres of shore and divers, and within 50 metres of swimmers and other boats.
Mr Clifford says Maritime NZ is funding the trial and working with the Marlborough Harbourmaster to show how speed guns could be used by other councils.
"The trial is going well," Mr Clifford says.
"The speed guns have good range and good accuracy, and other councils are keen to see the results we are getting."
Staff will be back on the water on Tuesday to catch more offenders.