Some communities have festivals in early May to sell plants and flowers for Mother's Day. Others celebrate the start of kids' baseball and softball seasons. Only North County would hold a festival for a dam.

The public is invited to attend Prettyboy Day at the dam on May 10 from 9 a.m. to 1 p.m. The second annual free event includes tours of the dam's gatehouse, exhibits, live music by guitarist Dave Huber, wildlife education by Scales and Tales, giveaways and prizes.

There are also games and crafts for kids, including a contest to accurately count the number of steps leading to the base of the dam. The Cruisin' Café food truck will be parked at the dam to sell food.

"Last year's Prettyboy Day was quite a success. There were cars parked on either side of the dam as far as the eye could see," said Kurt Kocher, Baltimore City Department of Public Works public information supervisor. He estimates 1,000 people attended last year's festivities.

Baltimore City owns the dam and reservoir, which holds 20 billion gallons of water. Prettyboy, Liberty and Loch Raven reservoirs together provide water to two million people in the Greater Baltimore metropolitan area.

Baltimore City has joined forces with the Prettyboy Watershed Alliance to sponsor the event.

The nonprofit Alliance, formed in 2003 to protect and restore the land and streams draining into the reservoir, will have several displays, said the group's president, Sharon Bailey.

"We have a big map of the watershed and will ask people to see if their properties are on the map," she said. "We have all sorts of information about ways people can improve the health of streams on their properties."

Last year, the Alliance coordinated the planting of 150 trees near the dam. This year, they'll demonstrate how to care for young trees, including wrapping last year's trees in protective sleeves.

She said George Lang, an Alliance member who lives near the dam, will bring his historical photos and newspaper articles that chronicle the dam's construction. The $4.1 million dam and reservoir project was completed in 1932.

Lang also has photos of the dam and reservoir that he took last fall during a helicopter trip.

Since the 7,000-acre watershed is in both Baltimore and Carroll counties, environmental agencies from both counties will have educational displays, too.

"I think there are a lot of people out who have memories of the early days of the dam and reservoir," Bailey said. "Plus it's a fun day for younger people, too. The dam transcends all age groups."

The event will be held rain or shine. Prettyboy dam is at 18100 Prettyboy Dam Road, Parkton.