Premise: Joe Knox was hospitalized, recovered, and still surfs in Imperial Beach. Like most, he takes precautions before entering the water. He'll check the county's water quality and the Tijuana River's flow online. He's also learned to read the ocean for signs of pollution such as discoloration on the water's surface, the consistency and color of the sea foam, and strange odors in the ocean breeze.
Hypothesis: The color of sea foam can indicate pollution.