Sydney’s Bondi Beach startled many swimmers earlier today when the water turned bright, arterial red, making it look like something from a “Jaws” movie.

The frightening color change may look like a hard-fought battle has just taken place, but it’s actually due to a particular strain of algae which blooms thickest in the summer. Australia, which enjoys opposite seasons from the U.S., is currently moving into warmer months.

The algae, which is sometimes called “sea sparkle”, isn’t harmful to humans but can irritate the skin after excessive contact. Plus, it smells really funky.

“It has got quite a fishy smell to it,” lifeguard Bruce Hopkins said. “It can irritate some people’s skin but generally not much more than that.”

Local authorities tested the water and closed the beach briefly, but it has since been reopened.