Some of it became entrained with sand and the sediment coalesced into mats that will stay submerged until they are weathered by the water or spotted by the Coast Guard.

When Skipper Rolando spotted a color line in the water, with deeper blue water on one side and greenish blue water on the other, he signaled to put lines into the water.

Cape Town's disaster management services had issued a warning hours earlier that sharks had been spotted in the water, but the shark flag was not flying.