PORTLAND, Ore. -- Two people skinny dipping during a stretch of particularly hot weather nearly cost Portland millions of gallons of drinking water.

Video: Incident Worries Residents

Two people were caught Saturday around 3 a.m. skinny dipping in a reservoir that provides most of Portland's drinking water, authorities said.

Portland Water Bureau officials said Ryan Langsdorf, 28, and Ashley Moyer, 23, were cited on trespassing charges after swimming in Mount Tabor Reservoir 6, reported television station KPTV in Portland.

Officials said the accused skinny dippers were found in a part of the reservoir that had been offline. Had it been in use at the time, the Water Bureau would have been forced to shut off the reservoir and consider dumping millions of gallons of water.

City officials took the same precaution earlier this year when a gallon of latex paint, a construction cone and hundreds of fliers were tossed in the reservoir.

Water bureau administrator David Shaff called the skinny dipping a "foolish act" that threatened the cleanliness of Portland's drinking water. He also said the swimmers could have drowned because of extremely cold water temperatures and a difficult rescue situation.

People who live in the area said the latest incident is part of a bigger concern.

"I felt all along they should cover it because I feel like it's a target for terrorists pouring some poison in," said Susan Spann, of Portland. "It wouldn't be detected until half of Portland is poisoned."

Officials were adamant in saying that it would be tough to poison 22 million gallons of water to the point where people would be affected.

However, new federal regulations will require cities to cover or bury their water supplies. Cities must have an approved plan by January 2009, which means it will take a few more years to see the changes.

In the meantime, Portland residents said something needs to be done.

"There are cameras around here, but security guards can only get here so quick," said Travis Turner, who lives in the area. "It does kind of worry me."