High winds on Monday night (20 Mar) have cause multiple boating accidents in both Riverton and Bluff, according the Environment Southland's (ES) Maritime manager Lyndon Cleaver.

A recreational vessel in Riverton Harbour sank after breaking its berthing lines in the high winds on Monday night, before drifting and colliding with the town's bridge.

The boat suffered severe damage, but ES advise no diesel was spilled at the time.

A Riverton boat sunk after slipping its moorings and hitting the town's bridge following high winds. Photo: Environment Southland

The boat remains grounded on the mudflats of Jacobs River Estuary, with the owner and insurance company now working on removing it from the estuary.

Another Riverton vessel also partially sank at its berth on Monday night, but was later refloated. 

And in Bluff a ship broke away from its berth and had to be recovered by South Port tugs.

There was also minor oil spill in Bluff as oil was being transferred, but ES report this was quickly dealt with.

A yacht also broke its mooring and became grounded at Green Point.

Earlier today ES activated a High River Watch on the Oreti, Aparima and Mataura Rivers following heavy rainfall in Southland headwaters overnight (21 Mar).

ES will continue to monitor river flows over the next couple of days as the increased flows make their way down the catchments, they said.