Concerned about aquatic invasive species that have popped up in other lakes across the country, Crater Lake National Park officials have temporarily closed the lake's pristine waters to scuba diving and the use of other water gear.

Concerned about aquatic invasive species that have popped up in other lakes across the country, Crater Lake National Park officials have temporarily closed the lake's pristine waters to scuba diving and the use of other water gear.

The closure will remain in effect until rules are established to minimize the risk of contamination from invasive species that include quagga mussels and other aquatic threats that could reduce the lake's world-renowned clarity and purity, officials said.

The rules, which will likely include a pemit system and require divers to take precautionary measures before diving, are expected to be in place before the beginning of the 2013 season.

At some 2,000 feet, Crater Lake is the deepest lake in the nation. The surface of the lake sits near 6,173 feet above sea level.

"We have seen the devastation to ecosystems and economies caused by the inadvertent introduction of invasive species from Lake Mead to Lake Erie," said park Superintendent Craig Ackerman.

"We want to prevent it from happening at Crater Lake rather than deal with the aftermath," he added. "The increasing popularity of the lake for scuba diving also increases the opportunities for divers and their gear to carry microscopic 'hitchhikers' into the water."

Although the invasive species may be tiny, the damage caused by introducing them into the lake is enormous and often irreversible, he noted.

In their native environments these species are often controlled by predators, parasites, pathogens, or competitors, he said.

However, when introduced to new environments such as Crater Lake, those same natural checks are often absent, giving the new species an advantage over native species and making them very expensive and difficult to control, he said.

"The risk is low but the consequences are high," said Mark Buktenica, aquatic biologist at the park.

The decision to temporarily close the lake to scuba diving and other water gear had nothing to do with the Aug. 13 swim across the lake — and back — by San Francisco residents Tony Lillios, 43, and Kate Howell, 29, Ackerman said. The two swimming adventurists, who swam without wet suits, are believed to be the first to accomplish the feat.

The closure notice had been posted at the lake on Aug. 10, three days before their swim, Ackerman said.

Swimming is allowed in the lake, although swimmers can enter and exit the water only at Cleetwood Cove and Wizard Island, he said.

September is the third busiest month of the year at the lake in terms of visitors, Ackerman said, noting that scuba divers have been in the lake when summer is drawing to a close.

"We haven't detected any invasive species yet," he said of species introduced by divers. "But once you detect them, it's often too late. Prevention is the most effective way to deal with an invasive species. They are very difficult to control once they are established."

Moreover, efforts to control them also could cause an imbalance to the lake's natural system, he said.

"This is the clearest natural body of water in the world," he said of large lakes. "That's a pretty high standard."

More than 100 years ago, the National Park Service introduced rainbow trout, kokanee salmon and crayfish into the lake, something that would not be done today because they also impact water purity, officials said.

But invasive species such as quagga mussels are much worse, Ackerman said.

"Quagga mussels had devastated the ecology at Lake Mead," he said of the Nevada lake. "They create entire populations that take over an area."

Not only would such an invasion impact the lake, but it would have a detrimental impact on the regional economy, he said, referring to visitations to the park.

In addition to the quagga mussels, other aquatic invasive species that could threaten the lake include the spiny water flea, and the viral hemorrhagic septicemia virus which causes severe and permanent damage to the habitats they invade by reducing the abundance of native species and altering ecosystem processes, officials said. Those invasive species rank among the most severe threats to biological diversity in bodies of water, they add.

Ackerman described scuba diving as a small but growing activity at the lake, thanks in part to increased adventure recreation around the globe.

"We really don't know how many scuba divers come to the lake," he said. "There have been no restrictions, no permit required."

Future restrictions likely will include a permit system, Ackerman said, although noting there are no plans to charge for the permit.

"By going to a permit system, we can educate divers on how to decontaminate their equipment to reduce the risk," he said, adding it also will allow them to discuss with divers the hazards of high-altitude diving.

"It will give us an opportunity to talk to the divers," he said.

To provide more information on aquatic invasive species, the Aquatic Nuisance Species Task Force, which includes the National Park Service, has created www.anstaskforce.gov/default.php.

Reach reporter Paul Fattig at 776-4496 or email him at pfattig@mailtribune.com.