Greta Bragg stayed as still as possible in the water, moving only to breathe through her snorkel. Raising her hands slowly, she began to scour the leaves of the weeds, one strand at a time.

Her target? A little gold beetle about half the size of a grain of rice.

Bragg, 19, is working with other high school and college students this summer to build a weevil population to combat Eurasian water milfoil in Christmas Lake, located in Shorewood and Chanhassen.

The group of a dozen or so volunteers is being trained to find the weevils, breed them in ideal conditions and spread their eggs throughout the lake. The itty-bitty bugs eat the milfoil, a stringy green nonnative plant that forms dense mats in lakes across Minnesota, making swimming and boating difficult.

“I’ve got one,” said Bragg, ripping off a strand of the weed with a weevil on it and stuffing it in a plastic bag.

“I’ve got at least 10,” said her brother Jacob, 14, who floated back to deposit his own bag of milfoil on the pontoon serving as the squad’s home base on the lake.

Equipped with flippers, goggles and wet suits, the Bragg siblings bobbed alongside their brother David, 17, and their neighbor Jerome Newhouse, 18.

Sallie Sheldon, a professor from Middlebury College in Vermont, popped her head out of the water. “I’ve got 15 or 20,” she said. “But I’ve been doing this for a while.”

Sheldon is teaching the group how to locate adult weevils, raise them in tanks and put eggs back into the wild. The weevil larvae eats the milfoil’s inside stem, causing the plant to collapse so it drops below the lake’s surface and making it less likely to grow back next year.

The group has a makeshift lab set up on the Newhouse family’s lawn — six large aquariums, some plastic kiddie pools, hoses, thermometers and microscopes, all under a large white tent.

It’s the easiest and cheapest way that Joe Shneider, president of the Christmas Lake Homeowner’s Association, can think of to tackle the lake’s invasive milfoil problem.

“You spend less money organizing and operating this program than some individual homeowners spend trying to manage milfoil at their dock,” he said.

The concept isn’t new. Sheldon researched biological controls for Eurasian water milfoil on Christmas Lake in the 1990s while completing her doctorate. After finding weevils to be an effective solution, she helped train employees from EnviroScience, an environmental services company, how to introduce the insects to lakes.

Christmas Lake bought weevils from EnviroScience back in 2013, Shneider said. Three years later, he said, you could barely find any milfoil on the lake’s glassy surface. The weevils were seen as an alternative to chemical treatments or mowing down the milfoil.

But EnviroScience stopped offering the treatment at the end of 2014 due to increased regulations and a hike in costs related to climate change. The weed has started to grow back in Christmas Lake.

But Shneider said this program should help fix that — and, more importantly, teach other Minnesotans how to fight milfoil. The group is documenting its work on a video, step-by-step.

“Other lake associations across the state and around the country can do this themselves,” Shneider said.

Sheldon will continue to work with the students for a few more days, then she’ll fly back home. The kids will be on their own for the rest of the summer, meeting for a few hours each week to count and cultivate the weevils.

Greta Bragg will return to Grand Canyon University in Phoenix this fall with a summer of research under her belt and a lab book to prove it.

“The fact that this is on my lake, the one I live on, makes it even more special,” she said.