There are fears that the water has made dogs ill and that pollution could be affecting wildlife in the area of the stream which runs through the riverside park between Hartford and the River Great Ouse. Both Anglian Water and the Environment Agency have been trying to find out why the water is changing colour and residents say investigators have told them they have been checking the towns industrial area. Dog walkers regularly use the area and have taken pictures of the water running a bright emerald green, blue, black and also foaming. Trish Brown, who walks her dog there, said: We always say What colour is it going to be today. She said her dog had been coated with diesel in what may have been a separate incident at the same place on the waterway. Anneke Tookman said dogs regularly went in the water under the bridge and hers had been sick after going in. We are just worried because it is all going into the river and polluting the water, she said. Pamela Dignam said: It is a beautiful brook and dogs are always playing in it and drinking it. She has banned her dog from going into the water. Pamela said Anglian Water was trying to find the source off the pollution and investigators told her they had been looking at the towns industrial areas. A spokesman for Anglian Water said: We are working closely with the Environment Agency to identify the source of the blue and green coloured water. We would always encourage customers to report any suspicious substances to us so we can investigate as soon as possible. We can be reached 24 hours a day, seven days a week by calling 08457 145 145. An environment Agency spokesman said: We are aware of the pollution incident on the River Ouse and are working with Anglian Water to identify the source. The river catchment covers a large area and there are numerous places where the coloured effluent could have come from. If people see the river change colour we would urge them to report it to our incident hotline on 0800 80 70 60 stating their location. This will help us in our investigations.