Heal the Bay does an excellent job at reporting and monitoring water quality in California.
This interactive map will show you live information from their test sites down to the exact beach.
It's pretty amazing that Temescal Canyon will have an F rating while 500 yds north the water quality gets an A. It basically gives you a red dot map of where all the sewer drains are! BTW, who knew Venice Breakwater was not a complete toxic wastedump! Ha!