At least four vessels ran aground between Tairua and Pāuanui recently due to a significant sandbar in the middle of the main harbour.

The Waikato Regional Harbourmaster said the sandbar formed due to severe shifting of sands that caused a safe secondary channel to disappear.

“We have had to remove the secondary channel markers which would usually mark a channel from the mooring zone direct to the harbour entrance ... unfortunately, there is no longer a channel there to mark,” they said in a statement on social media.

A Waikato Regional Council spokesperson said sand moved naturally in tidal estuaries through the action of wind and water, and the summer’s weather patterns contributed to the changes occurring in Tairua harbour.

“This is a natural event and has happened before. Changes in the weather will shift the sands and once there is again a secondary channel for safe passage, we will reinstate the channel markers.”

Launches and other vessels with deep draughts (distance from the waterline to the lowest part of the vessel) are recommended to travel only near high tide and exercise “extreme caution” around this area.

There is still a marked, safe channel from the Tairua ferry wharf at the Mary Beach Reserve, through the mooring zone and up to Pāuanui wharf.

From Royal Billy Point boat ramp onwards, the harbourmaster recommended boaties exercise caution because there is no marked channel.

“The dynamic environment with constantly shifting sands means we would encourage anyone traversing the harbour to take it slow, be aware of your depths and do your best to stay to visibly deep areas.

“We are actively monitoring the harbour, including gathering regularly scheduled aerial imagery to assess changes,” the statement reads.

When approached by the Waikato Herald, Thames-Coromandel District Council said it did not intend to dredge the affected area.

“Our council considers several conditions around dredging this area and these conditions have not been met,” a council spokesperson said.

“First ... the sand in the harbour is constantly moving. Any dredging could be undone almost as soon as it is completed, which would be a waste of ratepayers’ money.

“Second, dredging equipment and operators need to be booked far ahead of when they’re needed because of the high demand. It could be booked now, but conditions could have changed and the dredging not be needed by the time the dredging barge is in place.

“Third, there are resource consent conditions around the frequency of dredging in this area which mean we need to be careful to dredge only when the effects will be long-lasting.”