So the fish are actually made of cardboard, the leaking barrel is just an overturned garbage can and the submarine is a plastic structure made of plastic pipes on the bottom of a pool. These O'ahu high school students are making waves in the world of underwater robotic technology.

This weekend, student teams from Waipahu and Moanalua high schools will compete in the third annual national underwater robot challenge at the University of California at Santa Barbara.

At the competition, from Friday through Sunday, 40 high school and college teams will test their ROV designs in a timed underwater obstacle course that mimics real-world undersea exploration — the same sort of technology that scientists use when studying the reefs of the Northwest Hawaiian Islands or investigating shipwrecks like the Ehime Maru.

Both Hawai'i teams earned their spots in the national competition at the Hawai'i Underwater Robot Challenge at Waipahu District Park in December. This year's national event was organized by the Marine Advanced Technology Education Center (MATE) and the Marine Technology Society's ROV committee.

Over the past month, the five students in the Waipahu High robotics club have been planning, designing and trouble-shooting their box-shaped ROV, nicknamed "Was-Twisted-PVC."

Armed with recycled PVC pipes, plastic netting and model airplane parts donated by the high school and the UH Marine Center, they had to design and build a remotely operated device that could catch artificial fish, pick up rocks, and maneuver inside a model submarine — all while five feet under water. Because most of the materials were donated or recycled from past ROV models made at the school, the project cost the Waipahu High team about $200.

Waipahu High's ROV resembles a milk crate with an arm extending from the center. It has eight small propellers that push it horizontally and vertically in the water. A joystick, connected by a 30-foot tether of cables, controls the propellers.

The 18-year-old captain of the Waipahu team, Gibbson Tumaneng, said most of the students in the robotics club want to be engineers when they're older. "It's good practice," he said.

Tolentino, 15, said she became interested in robotics because her father is an engineer. "It's cool to see your ideas become a reality," she said.

The students also said they like underwater robot technology because it's less disruptive to the undersea environment than human exploration, and it can save lives.

"Sometimes you don't know what's going to happen," Tolentino said. "It's better to lose a machine than a life."

Although the Waipahu team placed third in national competition last year, this is the first national event for Moanalua.

"We didn't even know what ROV meant a few months ago," said David Izumi, a shop teacher at Moanalua High. "We're the only shop team as opposed to the other, engineering-focused teams. Ours may not be all fancy to look at, but it's functional."

The Moanalua team's ROV, named "Aquarius," resembles a miniature bulldozer with a flat, pointed grill across the front of an open mesh box.

"The scooper will act like a ramp for collecting rocks. It'll be faster that way," said team member Warren Garperio, 18.

Izumi said the students did their own research to solve technical problems, like achieving the right buoyancy to make the ROV hover in the water, rather than floating on the surface or sinking to the bottom. "The students learned in class about Archimedes' principle — about water displacement and buoyancy — and they used that principle in their design," Izumi said. The solution: two medicine bottles that can be filled or emptied of water to adjust the level of buoyancy.

George Huang, the Moanalua High team's pilot, said no matter what happens next weekend, his team has learned a long-term lesson about the value of teamwork. "It's not just about the ROV. Each of us thinks it's a really good learning experience to work as a group," Huang said. But in the short-term, he said the objective is clear: "to win."