The sea foam, like that on Ocean Beach Thursday night, is generated by the pounding surf, which is breaking down algae in the water and organic matter brought into the ocean by storm runoff.
It's something you might not want to touch, as it reportedly may cause skin irritations and breathing discomfort.
The foam is just one effect of the ongoing El Niño storms. Some streets in Ocean Beach are still covered with mud and sand, and many residents are still recovering from damage caused by flooding.
"Initially, I thought it was just the bathroom, no big deal, but then I walked barefoot on the carpet and went, oh great. We have people coming in tomorrow to fix it up," said Ocean Beach resident Charity Mulkey.
Lifeguards are also warning people to stay out of the ocean because of high levels of bacteria in the water.