It's a process known as upwelling, which plays out along the entire U.S. Pacific coast. Upwelling explains why water temperatures along California, Oregon and Washington beaches are much cooler than similar-latitude beaches in the East.
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There are two general reasons as to why the water temps are much colder on the West Coast compared to the East Coast. The first reason is because of the California cold current that runs along the coast from Canada to Central America. The second reason is upwelling.
But on that same beach, it's not uncommon to see kids shivering as they run out of the water, or a surfer wearing a partial wetsuit as they jog out for a session. California's ocean water is pretty cold, even in the summer, and it often catches visitors off-guard.
Not all beaches along the California coastline are recommended for swimming or wading. The very things that make these areas such spectacular places to look at and enjoy can be lethal to those caught unaware along the shoreline.
Warmest water – The ocean off Newport Beach and at Avalon on Santa Catalina Island typically heats up to 70 degrees F (21 °C) in August. Highest temperature year round – Long Beach has an annual daily mean of 65 degrees F (18 °C).
“So the reason why these beaches are usually dirty is mainly because of their limited water circulation, which leads to prolonged pollution near the shore,” Wu said. “This means the circulation is not enough to flush away all pollution when it happens.