In the shallow waters of Gijon harbour, in northern Spain, a large, yellow fish cuts through the waves.
But this swimmer stands apart from the marine life that usually inhabits this port: there’s no flesh and blood here, just carbon fibre and metal.
This is robo-fish – scientists’ latest weapon in the war against pollution.
This sea-faring machine works autonomously to hunt down contamination in the water, feeding this information back to the shore.
Here in Spain, several are undergoing their first trials to see if they make the grade as future marine police.
“The idea is that we want to have real-time monitoring of pollution, so that if someone is dumping chemicals or something is leaking, we can get to it straight away, find out what is causing the problem and put a stop to it,” explains Luke Speller, a senior scientist at the research division of BMT Group, a technology consultancy.
The company is part of the Shoal consortium, a European Commission-funded group from academia and business that has developed these underwater robots.
“At the moment, in harbours, they take samples about once a month,” says Mr Speller.
“And in that time, a ship could come into the harbour, leak some chemicals somewhere, then it’s gone, all the way up the coastline.
“The idea is that we will use robot fish, which are in the harbour all of the time, and constantly checking for pollution.”