Resident Gillian Marsden noticed a strange chemical smell in the Royal Park area on Saturday night and came across half a dozen silver gulls near the boardwalk at high tide around 5pm.

She said some birds were in the reeds and others were further out, in what appeared to be a slick on top of the water.

Ms Marsden said some birds didn't move, while others were struggling to flap about.

But when she returned to the area at low tide yesterday morning, the birds were gone.

"It was quite a chemical smell, which you could taste in your mouth," Ms Marsden said.

"But I don't think it was diesel, because of the smell.

"The birds were feeding at that time.

"There were a couple which were not moving.

"The most disturbing one was the bird which couldn't fly and it collapsed back in the water and could not keep its head up.

"It was quite scary."

Ms Marsden reported what she saw to the Environment Protection Authority, and was told the matter would be investigated.

She recommended people call the EPA on 1800005171 to report pollution incidents.