The fishing ship Astrid, said to be the source of an alleged sewage spill that closed Pilot Bay's beach today, has been detained by Maritime New Zealand for safety reasons.

A surveyor has assessed what repairs are required to make the ship safe to move to drydock, says Vince Cholewa at Maritime NZ.

The trawler Astrid detained in port.

'It is detained but it has not leaked sewage into the harbour,” confirms Vince.

It previously discharged its sewerage tanks while at sea and they were empty, he says.

'For some reason, once in the harbour a leak developed in the hull, and the reason it's detained is for safety reasons.

'It is being surveyed so it can be patched up, so it can be moved to dry dock where it can be properly fixed.

'It did discharge water, but it was not sewage because the sewerage tanks were empty.”

Exactly where the ship is repaired – expected to be either Auckland or Lyttelton – depends on the owners' decision.

The Marine Traffic website states Astrid is a New Zealand-flagged trawler at 3,413 gross tonnes and 97m long, built in 1985 with the home port of Lyttelton.

The Port of Tauranga website has Astrid scheduled to sail tonight for Las Palmas at 6pm. Astrid is owned by Astrid NZ Ltd, a wholly owned subsidiary of Vela Fishing Ltd.

The city council ordered Pilot Bay beach closed to swimmers today as a precaution.

The results of subsequent water samples taken are expected to be known tomorrow.