SAN DIEGO (CNS) - An unusually powerful rip current pulled between 50 and 75 swimmers from the surf off La Jolla Shores Thursday afternoon and into deeper ocean swells, where more than two dozen of them wound up treading water and stranded, until a contingent of lifeguards came to their rescue.

The large-scale beach emergency occurred about 2:45 p.m., when three typical-sized outward-flowing channels of water merged into a single big one, creating a hazardous and "pretty unusual dynamic," said San Diego lifeguard Lt. Nick Lerma.

The combined current took hold of everyone in the water off a roughly 100-yard stretch of shoreline, though all but 26 of them eventually were able to make their way back to land on their own, Lerma said.

Those unable to swim free were aided by about a dozen lifeguards -- several of whom had to come in from other city beaches -- equipped with paddle boards, floatation buoys and personal watercraft towing "rescue sleds."

Though no serious injuries or medical crises resulted from the mega-rip, "it was an intense situation for about 10 or 15 minutes," Lerma said.

Lifeguards closed the affected section of shoreline until further notice as a safety precaution.