The Environment Protection Authority (EPA) says fluoride from Alcoa's aluminium smelter at Portland is making kangaroos sick.

Fluoride from a nearby alumininum smelter is making Portland kangaroos ill. (ABC Local : Margaret Burin )

The EPA's Bruce Dawson says the fluoride is being absorbed by the nearby vegetation which is then being eaten by the kangaroos.

He says the fluoride poisons the kangaroos and makes lesions grow on their bones, which renders them lame.

"Once kangaroos have restricted movement [it] has a significant impact on their welfare. So this is something that needs to be managed and avoided."

He says there is not a lot of information around about the impact of fluoride on kangaroos.

The problem is more common in cattle.

"There was a lot of research done in the 60s and 70s in the United States but this really has just started to emerge in terms of the impacts on kangaroos."