Sappers Bridge in Walpole Nornalup National Park, Western Australia, was completely covered by white foam from the Frankland River last weekend.
According to the Department of Parks and Wildlife, the foam was a naturally occurring event caused by high water levels and tannins in the river.
“As the water is agitated, it becomes caught up under the bridge and creates foam,” the department said.
The department added that staff tried to remove some of the foam, with limited success. The foam phenomenon only occurs during high rainfall years and lasts just a few days, so it has since cleared from the river.
There's a short video here.