At Tutukaka, an Auckland man with a young passenger had been reported driving a jetski at more than 20 knots past moored boats in the harbour on January 4.
The rider had been issued with a written warning that jetskis have a 5-knot speed limit within 200m of the shore or 50m of another vessel, craft or person.
Mr Surendran said jetski registration was compulsory under the Northland Regional Council's navigation safety bylaw. People flouting the bylaw risked an instant fine of $200.
"As well as helping locate anyone seen breaking our safety bylaws, registration is also a useful way of identifying jetskis if they're stolen."
By mutual agreement over the past few years, the Auckland Council maintains a single register of jetskis used in the Auckland, Northland and Waikato regions.
Registration costs $35 and involves completing a form available from regional councils or their websites.
Registration with the Auckland Council is valid in all three regions for the life of the jetski. The registration number needs to be displayed on each side of a jetski. Stickers can be supplied for $12.50 or the number can be signwritten on the jetski by the owner so long as each digit is at least 90mm high and 80mm wide and clearly visible.