About a hundred boats turned out in Marlborough Sounds on Saturday, in protest at the speed of the interisland ferry Kaitaki.
About 25 boats began the demonstration at the entrance to the sounds, Tory Channel, and the numbers swelled as the ferry neared Picton harbour.
The police and coastguard kept protest away from the Kaitaki, but observers said the protest was peaceful and orderly.
Many carried flags, some saying 'Citizens Arrest' and "Toll No Respect".
Toll New Zealand denies the Kaitaki's usual speed of 18 knots causes its wake to damage the shoreline and endanger small craft.
The Marlborough District Council has set a speed limit of 15 knots.
An environment court hearing is currently underway as Toll Shipping appeals against a speed restriction on its new interisland ferry.
Toll Shipping claims it has an existing right for the Kaitaki to travel at higher speeds and has taken its case to the environment court.
In his opening submission Toll's counsel argued the shipping industry will lose $42 million a year if the speed limit stays at 15 knots.
Toll says it wants to be free to sail the new ferry at 20 knots, but with a monitoring programme in place so if there are any adverse effects it will slow down in specific areas.
The company says there is no proof of lasting environmental damage in the Marlborough Sounds from the wake of conventional interisland ferries, there is no grounds for the council's environmental concerns and its speed rule should be revoked.
The Department of Conservation is supporting the 15 knot rule and fears for the future of the Sounds if it is lifted.
"They (ferries) do have a biological impact and we know that because there is a recovery, which we can show from data and research that the department's done from controlling the speed of the fast ferries and their wake," says DOC lawyer Camilla Owen.