The 50-year-old needed to use a toilet while on a social club outing in Nelson on Saturday evening and found cubicles near the Visitor Information Centre locked.

She took shelter behind bushes but slipped, plunging down to the rocky river bank about 6.30pm.

Panicked onlookers raised the alarm.

Country Fire Authority (CFA) members Daniel Sylvester, 16 and Dylan Whitehead, 20, among the first on the scene.

Daniel's father Stephen is the Nelson CFA captain and was also called to help.

"She was pretty lucky really that the tide wasn't in," he said.

"If it had been up she would have been floating and anything could have happened."

Mr Sylvester said his son and Mr Whitehead were bringing their boat in after an afternoon of fishing when the accident happened.

"They were just putting their boat back in the shed when they heard screams and got asked to go back around the corner to see what was going on," he said.

"They came up to her and got a pretty big shock. Other blokes by then had scrambled over the bank and were making her comfortable."

Two ambulances from Mount Gambier attended, with the south-west rescue helicopter arriving half an hour later.

The woman was taken to the Royal Melbourne Hospital with several fractured ribs and is expected to return to Warrnambool within the next two days.

"She would have been in trouble if the locals weren't there," Mr Sylvester said.

"In the position where she was, you wouldn't know what would have happened."

The CFA captain said the cliff had not been the scene of other falls and wasn't the subject of community concern.