Early indications are that the ecology of the River Worth has been seriously affected by last week's foam pollution.

Officials from the Environment Agency say that samples taken from the river show that large numbers of invertebrate organisms, used as a guide to the assess the severity of pollution, have died as a result of the pollution.

A spokesperson for the Environment Agency said: "We did take samples from the river and there was a high mortality rate in the sample which included mayfly and caddisfly. Both are pollution sensitive and so are good indicators. Also several small fish, called bull heads, were found dead."

The spokesman added: "I believe a 500-metre stretch of river was affected. At this time, we anticipate it will take at least three to four months to re-colonise this stretch of river so we are treating it as a very serious incident."

Officials at the Environment Agency are also looking into the cause of the pollution, which at this stage is believed to be a detergent. A spokesperson said: "We have traced the source of the pollution and we will be calling in the site owners for a formal interview. We will then be putting all our evidence together to decide whether to pass it on to our legal department but it is too early to decide if there will be any prosecution."

Lawrence Brocklesby, president of the Keighley Angling Group, said that although he has no reports of dead fish from club members it is still cause for concern.

He added: "I haven't had any comments from our members at all. Having said that, that doesn't mean there aren't any.

"It could affect the River Aire as the River Worth obviously flows down into it."

Danny Parker, owner of the Bronte Park Caravan Site, through which the River Worth flows, said he has not seen any dead fish in the river.

He added that a private prosecution was not out of the question if the Environment Agency can prove who is responsible.

Mr Parker said: "If we find any dead fish in our stretch of river I will take legal advice. By doing that I will be backed by the National Rivers Authority."

Mr Parker, who annually restocks the river for the benefit of fishermen and holidaymakers, added: "If they have a good case then we will have a good case."

Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.