SYDNEY (AFP) - An algal bloom the size of the southern Australian island of Tasmania has been stirred up in the wake of tropical cyclone Rusty, an expert said on Wednesday.

The powerful storm hit Western Australia last week, bringing torrential rains and wild seas to the major iron ore hub in the resource-rich Pilbara.

In its wake it has created a massive bloom of algae produced by the agitation of microscopic plants or phytoplankton, University of Western Australian oceangrapher Charitha Pattiaratchi said.

"Basically it's an algal bloom. It's not harmful," he told AFP.

"At the moment it's the size of Tasmania," he said, referring to the Australian island with a mainland area of 64,519 square kilometres, about the size of Latvia or Sri Lanka and a little smaller than Ireland.

Pattiaratchi said tropical cyclones were known to cause blooms, but this one was unusual in size.

"This one is big," he said, adding that remote-controlled underwater gliders measuring elements such as water temperature, salinity and how much phytoplankton was in the water had been operating during the cyclone.

Pattiaratchi said the measurements such as changes in temperature during a storm could be useful in forecasting the path of tropical cyclones, particularly for the industry area of the Pilbara.

"The glider gives us an opportunity to collect data under extreme conditions," he said.