Using apples, colorful Twizzlers, cream cheese frosting and sugary sprinkles, about 50 Broward County Girl Scouts created their own edible underwater reefs Saturday during a presentation on how to protect the environment.

The event, held at Oleta River State Recreation Area in North Miami Beach, was put on by four students -- all senior Girl Scouts -- from South Plantation High's Everglades Restoration and Environmental Science Magnet Program.

Lessons about beach erosion, pollution and how to test water quality kept the attention of the audience of young Girl Scouts.

''I'm going to tell all my friends and neighbors not to pollute,'' said Allison Weigel, 10, a fourth-grader at Fox Trail Elementary in Davie. ``It's really bad for the Earth and the animals.''

The project is the brainchild of 17-year-old Rebecca Schultz, a senior at South Plantation High.

While scuba diving three years ago, Schultz found the underwater reefs ``deteriorating and dying.''

''It bothered me,'' she said. ``There wasn't much to see anymore and I wanted to know why.''

So she started researching and discovered the biggest threat to the reefs was pollution from humans.

Schultz read about artificial reefs -- made of tires, concrete and boats -- and decided to make her own version.

Schultz and three classmates -- Jasmine Jeffers, 16, Veronica LaFranchise, 17, and Sara Yinger, 17 -- created two sets of the reefs out of concrete. In March, the ''reef balls'' -- round, heavy masses -- were placed in the water at Oleta Park, a mile off shore near Golden Beach.

The girls regularly check on their artificial reefs, with hopes that they will help stimulate the growth of living reefs.

But their work didn't stop there.

With $35,000 in grants they have received from various organizations over the past two years, the girls have organized four free workshops aimed at teaching Girl Scouts and Brownies how to protect the environment.

During Saturday's four-hour event, the young Girl Scouts took water samples from the estuary and tested it for nitrates and phosphates, examined the differences in the density of salt and fresh water and signed a water conservation pledge. They also played with snails, made colored drawings of how to protect the environment and swam.

Schultz and her friends are compiling the activities into a booklet to distribute to Girl Scout leaders in Broward and Miami-Dade counties, with hopes that they will do them to their troops.

For many of the girls, the highlight of the day was the create-your-own reef activity.

The apples represented the skeleton of the reef, the frosting doubled as limestone, the licorice were the polyps and the green sprinkles served as algae. The girls examined their creations as they bit into them.

''I love apples. No, I mean, I love reefs,'' said Karina Forler, 11, a sixth-grade student at Silver Trail Middle in Pembroke Pines, as she wiped leftover icing off the tip of her nose.

G.G. Pacetti, 9, a fourth-grader at Virginia Shuman Young Elementary in Fort Lauderdale, said the experience is one she won't soon forget.

''It's so fun because we got to swim, we're learning a lot and doing a whole bunch of cool things,'' she said.

''It's all about water -- and I love water,'' Pacetti added.

For Jeffers, juggling school work, college applications and a social life, while organizing the environmental program can be tough at times. But, she said, it's well worth it.

''It's a lot of pressure and a lot of work,'' she said. ``But it's really rewarding.''