Oily Sheen
After the first rains of the year , creek water is sometimes covered with an iridescent sheen . As rain washes over streets and parking lots it picks up oil and carries it to a storm drain . Seeing a sheen at times other than after the first rains could indicate a more serious problem .
Foam from Synthetic Sources
Foam bubbles from substances like detergents and phosphates have an iridescent sheen . This foam does not break apart easily . Consequently , it lasts longer and can travel farther downstream than naturally occurring foam .
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