The 5-foot-long robots work by mimicking the swishing movements of a fish's tail, according to University of Essex robotics expert Huosheng Hu, whose team is manufacturing the machines.
He said the robo-fish would be equipped with sensors to monitor oxygen levels in the water, detect oil slicks spilled from ships or contaminants pumped into the water from underground pipes.
The robotic fish will patrol the harbor of Gijon, in northern Spain under a $3.6 million grant from the European Union. Hu said Gijon was chosen because port authorities there had expressed an interest in the technology.
The plan might seem "like something straight out of science fiction," said Rory Doyle, a researcher working on the project, but he explained that there was a very simple reason for choosing fishlike machines to monitor the harbor's environmental health.
"The design of fish which nature has produced is a very energy-efficient one," Doyle said. "The fish's efficiency is created by hundreds of millions of years' of evolution. Submarines come nowhere near it."
Information gathered from the robo-fish would be transmitted to the port's control center using a wireless Internet signal when the devices surfaced. The data gathered would be used to create a three-dimensional pollution map of the harbor's area.
The fish won't need remote guidance - their sensors can help them avoid obstacles such as rocks or moving ships, said Doyle, who works for the engineering consultancy BMT Group Ltd., a member of a consortium manufacturing the machines.
The fish can also swap navigational information with each other using a form of sonar. When their batteries are nearing the end of their eight-hour capacity, they can swim back to a power hub to recharge.
Each fish costs about $28,000 to make, and BMT estimated their maximum speed at about one yard per second.
A smaller version of the robo-fish began swimming around in a special tank at London's aquarium in 2005, wowing visitors with its lifelike movements and brightly shimmering scales. Hu said the new fish would have to be bigger to withstand higher water pressures and powerful Atlantic tides.
Hu said he hopes to release the robo-fish into the water within the next 18 months. He didn't know precisely what the machines would look like or even what they would be made of, but he acknowledged the bigger fish probably wouldn't have the charm of their showy, blue-and-silver aquarium-dwelling cousin.
"This project's more focused on robustness," Hu said. "Appearance doesn't have a high priority."