The hottest beach in Washington County isn't on a lake or river, but surrounds a manufactured pond in the middle of Lake Elmo Park Reserve.

The swimming pond opened for the season on Memorial Day weekend and, despite fickle weather, drew hundreds of people to its sandy shores and colorful "funbrellas" that surround the 2-acre complex.

"I've had Hennepin County come out here and say, 'Wow, we've never seen a beach like this,'" said Mike Polehna, the county's parks manager. It's one of only three such manufactured beaches in the metro -- and in Polehna's opinion, the most popular.

Lake Minnetonka Regional Park has a similar beach and swimming pond, as does the Three Rivers Park District in Plymouth, he said. The Lake Elmo beach was built in 1986.

"It was pretty unique at the time in the state," Polehna said.

The beach attracted about 68,000 people in 2010, the most recent year that confirmed numbers were available. That's 10 times the turnout at the county's newest beach at Big Marine Lake, about five times more than Square Lake, and dwarfs attendance at smaller county beaches at Point Douglas and St. Croix Bluffs Regional Park.

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Among those spending Memorial Day at the Lake Elmo Park Reserve swimming beach was Mackenzie Knauff, 11, of St. Paul Park.

The Lake Elmo pond is far safer than swimming in the nearby lake, which is one of the deepest in the metro at 140 feet and has steep dropoffs not far from shore.

Surrounded with sand for more than 1,000 feet, the swimming pond is shaped much like an oblong bowl with shallow water around the entire perimeter. The deepest part, in the middle, is about 6 feet.

Five filters and four 50-horsepower pumps circulate 1.8 million gallons of water through the pond every day, "just like a swimming pool," Polehna said. The county employs eight to 10 lifeguards and often other workers to direct traffic and parking on the busiest days, which generally peak on the July 4 holiday.

"It gets very crowded," Polehna said. "People walk half a mile to get to the beach."

Lifeguards count people at the beach twice a day. Swimmers have to leave the water every hour for "safety breaks" and parents are reminded to accept responsibility for their children, he said. Some parents, he said, think of lifeguards as babysitters who should follow children into concessions, parking lots and playgrounds.

"We've been really strict on making sure people watch their kids," he said. "That's not the lifeguards' job. Their job is to react to emergencies."

About 616,000 people visited the Lake Elmo park -- which has trails, camping, fishing and other activities -- each year. That's the largest attendance of any county park. Overall, the county's eight outdoor parks attracted more than 1.6 million visitors in 2011.

Last Sunday and Monday, more than 5,000 vehicles entered the park, bringing an estimated 18,500 visitors. A count of how many of those people went to the beach wasn't available.

Kevin Giles • 651-925-5037 Twitter: @stribgiles