There are plenty of descriptions for it.
"Very slimy, very slimy," said Seal Beach resident Michael Pless, who owns M&M Surfing School. "It didn't have much of a smell.
"It's a very yellowish, green algae-type appearing substance," said Lt. Mike Beuerlein of Huntington Beach's Marine Safety Operation.
"Maybe a little more lime," Aquino said. "Looks toxic."
Lifeguards said the unusual substance has been spotted on and off for several weeks, from Seal Beach to San Onofre State Beach.
Some days it's more visible than others.
"It kind of runs parallel to shore an it's never more than 10 to 30 yards in width," Beuerlein said.
So far, no one knows for sure what it is. The Orange County Health Care Agency is conducting tests.
"You don't want to ingest anything you see out there but they're still testing it," Beuerlein said. "All tests have been negative."
There has been no evidence of bacterial contamination, but Pless's surf school took precautions.
"I was concerned," Pless said. "It was that thick and I told everybody we need to move."
Others are choosing to stay on the sand.
"I wouldn't want to go in there not knowing what it is," Aquino said. "It's too disturbing. I don't want to take any extra chances I don't have to."