Swimmers and beachgoers were advised to remain on alert on Wednesday and, in some places, avoid going into the ocean.

The culprit for this sneaker wave threat is what's called a long-period swell arriving at beaches on the Northwest coast, which is generated by large, sprawling storms in the Pacific Ocean.

A massive 12.34-metre wave was recorded off Main Beach on the ... As Cyclone Alfred approached the Queensland coast, ocean buoys at the University of Sydney One Tree Island Research Station ...