PARENTS are being urged to keep children away from a poisoned North-East river in which thousands of fish have died.

An invisible and odourless pollutant has killed most of the aquatic life in a stretch of the River Tame and its tributary, Main Stell, between Middlesbrough and Stokesley, in North Yorkshire.

The pollution is extensive, covering almost ten kilometres.

Thousands of minnows and stone loach, and hundreds of trout, eels and rare lamprey have been spotted floating on the surface.

What is alarming the Environment Agency most is the high number of eels that have been poisoned.

A spokeswoman for the agency said last night: "Eels are very tolerant of lots of different types of pollution.

"The fact they have died says a lot about either the concentration of what has gone in there or the sheer volume.

"We don't know what has gone in there. If it has killed stuff which is pollution tolerant, God forbid a child or a dog goes in there until we have found out what it is."

Samples from the river were last night sent to forensic laboratories for tests.

Officials from the Environment Agency and the Government fisheries department spent the all yesterday investigating.

The will return to the rivers today to conduct surveys and to carry out dye tests on outfalls and drains, in a bid to find the source of pollution.

The agency spokeswoman added: "We believe we may have found a source. We can certainly say there is a narrowing of the point of source.

"We are fairly sure this is pollution-based. This is something which has got into the river and something we use as a starting point."

The number of dead trout and lamprey indicates the water was of a relatively high quality before disaster struck.

James Parker, environment management team leader, said: "We started investigating the source of the pollution as soon as it was reported, but it is odourless and has not discoloured the river much, so the water may look normal.

"We're currently looking for the source of the pollution."

Although not linked, the Tame incident is similar to recent serious pollution of the River Skerne, at Darlington, which killed many fish and is still being investigated.