When an approaching thunderstorm threatens swimmers at Greenbrier State Park, lifeguards reach for an iPod, scroll through the menu and press play.

"La tormenta se aproxima," says the recording amplified by the loud speaker system. "Todo el mundo salga del agua."

With that, hundreds of people move toward shore.

The staff at Maryland's state parks, destination for 11 million visitors last year, is learning to adapt to a rapidly growing and enthusiastic clientele: Hispanic families.

They come early, stay until closing and are repeat customers, say state park officials.

According to the latest U.S. Census figures, the largest spike in the last decade was in the state's Hispanic population, which more than doubled to 470,632. Roughly one in 12 Marylanders is Hispanic.

And while an economic impact study last year by the Department of Business and Economic Development showed that just 2 percent of day-use visitors were Hispanic, park officials say that paints an incomplete picture. Hispanic families concentrate in a handful of waterfront parks near the Baltimore-Washington corridor.

For example, at Greenbrier in Washington County and Sandy Point State Park outside Annapolis, as many as 80 percent of the picnickers and swimmers are Hispanic, officials at the two sites say. Day trippers also favor Seneca Creek State Park in Montgomery County and the Hammerman area of Gunpowder Falls State Park in Baltimore County. When those fill on busy summer weekends, families drive to Cunningham Falls north of Frederick or Point Lookout in St. Mary's County.

"This isn't just a Greenbrier or a Sandy Point story. It's spreading and becoming a Maryland story," says Nita Settina, superintendent of the state's 66 parks. "They want to do all the outdoors things they did in their native country in their new home. It's up to us to make them feel welcome."

To meet the needs of the Hispanic visitors, parks have added translators, posted bilingual signs and stocked park stores with ethnic foods. Staffs are getting cultural training and will be taught basic Spanish commands and phrases before next season to help ease the communications barrier.

Other ethnic groups have gravitated to specific parks, mostly by word of mouth: Koreans at Point Lookout, Russians at Cunningham Falls and Africans at Patapsco Valley, just south of Baltimore. That has required additional adjustments by park staff, says Ranger Jen Cline of the Maryland Park Service Training Division.

Cline says on Memorial Day weekend, she encountered some African men with a blow torch at a Patapsco Valley pavilion.

When questioned, the men told Cline, "We have to sear the goats."

Not knowing whether park rules prohibited the searing of goats with a blow torch before barbecuing, but deciding it might be a safety hazard in a full park, Cline asked if they could finish up quickly and put it away. Everyone was satisfied.

"You just have to put yourselves in your guests' shoes," Cline tells her trainees.

That includes making allowances, when possible, for lakeside baptisms and seasonal religious celebrations, too.

A survey of 500 Greenbrier visitors showed the predominant countries of origin are: El Salvador, Guatemala, Mexico and Honduras. They drive one or two hours to get there, stay an average of 8 hours and visit as many as a half dozen times a season.

The new visitors have prompted a rethinking of park procedures and designs that are 30 to 40 years old, says Lt. Tammy McCorkle, who has been at Greenbrier for 11 seasons. For example, people begin lining up at 3 a.m. to get in and secure one of the prime shaded picnic tables near the water. By 8, the line backs up nearly two miles on U.S. 40, forcing staff to open early to alleviate a traffic safety hazard.

Gone are the days when one vehicle with four or five family members was the standard. Now, an informal survey shows, the average group size is 15 people "who stay until closing," McCorkle says. "That means the traditional picnic pad, with one table and one grill, is useless to our visitors, a poor design. You have to have room for four tables."