PORTLAND (AP) – There are plenty of plenty of people on the beach this summer at Wells Beach. There just aren’t many swimmers.

That’s because ocean temperatures off Maine are even colder than usual.

“Our water temperature was only 62 degrees (Thursday) and that’s because it warmed up in the last few weeks,” said Nikki Roux, a lifeguard in Wells. “A couple weeks ago it was giving you a headache it was so cold. Within a minute your legs would be numb up to your knees.”

An analysis of temperatures collected by the Gulf of Maine Ocean Observing System at a monitoring buoy in Casco Bay shows that water temperature in the first week of August averaged less than 63 degrees compared to more than 66 degrees last year.

That may not sound like a big difference – until you try swimming in it.

The cold waters aren’t contained to Maine. People at a number of beaches along the East Coast have noticed a sharp drop in water temperatures. So many people have contacted the National Oceanic and Atmospheric Administration that William Tseng, an oceanographer at NOAA’s Silver Spring, Md., headquarters, is investigating.

He’s examining three possible causes: increased river runoff from this spring’s frequent rains; a current of cold seawater snaking down from the North Atlantic; and an event known as “coastal upwelling.”

While Tseng and other researchers caution that it’s only a guess, the prime suspect appears to be coastal upwelling, a phenomenon that occurs when persistent winds blow up the coast from the south or southwest.

The winds push away the warm surface layer of water, which is then carried eastward and replaced by colder water below the surface.

But apparently there is an upside to the chilly waters. It was about this time last year when sharks showed up at Wells Beach, causing swimming to be banned for several days.

Roux remembers that it was warm waters, in the lower 70s, that caused the sharks to come to shore.

AP-ES-08-08-03 0216EDT