Fresh water off King George Sound forms ‘Moses Line’

It might look like an oil slick but these photos, taken from Marine Drive overlooking King George Sound last week, show what can happen when fresh water meets salt water.

The border between fresh water and salt water is sometimes called the Moses Line, taking its name from the prophet Moses and the parting of the Red Sea.

The meeting of lower-density fresh water and higher-density salt water is typically seen on the south coast when an inlet is opened to the ocean.

In the case of King George Sound, it occasionally becomes noticeable in still conditions and after significant rainfall.

Albany Sea Rescue vice-president and Albany Tug Services owner Colin Bairstow said it was rare for the effect to be so clear.

“Fresh water comes down the King River or Kalgan River and gets flushed out through Oyster Harbour and pushes out into the salt,” he said.

“That line the other day, we sat on the line where the fresh water met the salt water and we actually went out with it.

“That does happen in wintertime but not usually to that extent.”