HUNTINGTON BEACH, Calif. (KABC) --Brownish foam moved with the waves in Huntington Beach over the past week.
"The last four or five days it's been thick out there," said Huntington Beach resident Mark Marino, as he fished off the Huntington Beach Pier.
"It was kinda slippery, it had kind of a green look to it, so it was kinda weird," Josiah Sabala, a surfer from Buena Park, said.
A weird look and smell, the slimy gunk showed up along parts of Orange County's coastline.
"It's kind of oily," said Marino. "It's gross, I'm thinking it's like bilge from a ship or something."
"Some people are thinking it's because of the hot water and climate change. I have no idea what it is though," said Huntington Beach surfer, Tijani Frederick.
Lifeguards say they've been overwhelmed by calls from people wondering what the foam is.
"All it really is, is this algae," explained Huntington Beach Marine Safety Lt. Claude Panis. "We've had an algae bloom. Algae dies off, it drifts into the surf."
Lifeguards said high surf last week agitated the water, creating an algae-based sea foam.
"It's like a decaying plant, it's plant life. It's a normal natural occurrence," said Panis. "I've seen it in cycles over the last 38 years, probably 10 or 15 times."
The Orange County Healthcare Agency regularly tests the water. Authorities said it's safe to enter the water as the foam is not dangerous.
Lifeguards said with the smaller waves Friday, just 1 to 2 feet, they were seeing less of the brown gunk, but that could change if a storm comes in and the surf grows.
"Because the algae is still out there, if you agitate the water and stir it up, we'll likely see an increase in the sea foam again," Panis explained.