UK scientists have designed a new way to detect water pollution - by building large robotic fish to swim in the sea and track down pollutants.

The carp-shaped fish, which are around 1.5 metres (5ft) long, are equipped with chemical sensors which can detect the source of pollution such as leaks from vessels.

The fish do not require remote control, but have their own navigational abilities allowing them to swim independently and return to their hub to be recharged when their eight-hour battery runs low.

The fish are being developed so they can search underwater for chemicals dissolved in the water as well as pollutants such as oil on the surface.

Five of the fish-shaped robots are to be released into the port of Gijon in northern Spain as part of a three-year research project funded by the European Commission and co-ordinated by engineering and risk management consultancy BMT Group Ltd.

The fish, which will cost around £20,000 each to make and will swim at a maximum speed of around one metre per second, are being built by Professor Huosheng Hu and his robotics team at the University of Essex.

It is hoped that if the project is successful, the fish could be used in rivers, lakes and seas across the world to detect pollutants.

Prof Hu, who hopes to release the robots by the end of next year, said: "We are designing these fish very carefully to ensure that they will be able to detect changes in environmental conditions in the port and pick up on early signs of pollution spreading, for example by locating a small leak in a vessel.

"The hope is that this will prevent potentially hazardous discharges at sea, as the leak would undoubtedly get worse over time if not located."

Rory Doyle, senior research scientist at BMT Group, said: "In using robotic fish we are building on a design created by hundreds of millions of years worth of evolution which is incredibly efficient. This efficiency is something we need to ensure that our pollution detection sensors can navigate in the underwater environment for hours on end."