The bream were found dead in a pond at Loxwood on the Sussex-Surrey border.

The Environment Agency thinks the chemical entered the pond over the weekend from a neighbouring field, which has now been contained.

But it says it is concerned for other wildlife in the area and is asking people to keep away from the polluted water.

'Stay away'

Laboratory analysis carried out by Environment Agency scientists confirmed the fish were killed by the chemical.

The agency has contained the toxic herbicide by placing sand bags at both ends of the pond.

It says it is now considering various ways of cleaning it up and will be advising the landowner.

Environment officer Emma Daniels said: "We would urge people to stay away from the pond for the next few days and would ask people not to feed the ducks there.

"Bread or other foodstuffs that are thrown into the water will absorb the herbicide and could then poison wildlife or pets."

The Environment Agency has fenced off the pond and put warning signs near the site.