As summer heats up and people head to lakes and beaches, jetski owners are being reminded to stick with safety rules, including not allowing unsupervised young people to ride the machines.
Northland's deputy Harbourmaster Chidambaram Surendran said complaints about jetski users' behaviour typically increased at this time of year, with most complaints centred on speeding and jetskis being driven too close to other boats or people.
"We've had a number of fairly serious incidents around the region so far this summer, including one young man who allegedly travelled into a marina at speed on a jetski and another where someone allegedly raced closely past a number of moored boats."
Other incidents had included children being towed behind jetskis on a biscuit without a proper lookout and others travelling at speed very close to rocks or riverbanks in narrow coastal areas.
Owners were also reminded to register their jetskis, which was useful to identify them if stolen.
Mr Surendran said it was illegal to use unregistered jetskis in Northland waters and people flouting the bylaw risked an instant fine of $200.
Legally, people under 15 could not operate vessels capable of speeds of more than 10 knots (including jetskis) unless they were being actively supervised by an adult.
"That doesn't mean an adult standing on the beach watching; the supervisor has to be older than 15 and be within 'immediate reach' of a machine's controls," Mr Surendran said.
All jetski users should take care not to exceed 5 knots within 50 metres of another vessel or person in the water, 200 metres of shore or a vessel engaged in diving.