Vandals who shoved three huge chunks of wood down a manhole are being blamed for a major pollution incident in Keighley.

Scores of fish died when raw sewage poured into the River Worth.

This week water company bosses said a sewer blockage, due to the wood, was the cause.

And they revealed that such incidents of vandalism are not uncommon -- everything from electrical equipment to ironing boards has been discovered dumped down shafts.

Now Yorkshire Water (YW) is appealing through the Keighley News for the public to report anyone spotted tampering with manhole covers.

The company's rapid response team managed to clear Sunday's blockage soon after being alerted to the situation by the Environment Agency.

But not before sewage spewing into the river had polluted a 2km stretch of the watercourse, killing an estimated 100-plus fish.

Nigel Wade, who led the response team, said: "We arrived on site within 45 minutes of being informed about the situation. The speed at which you respond to a pollution incident is very important -- the quicker you can stop it happening, the less damage it will cause to the watercourse and wildlife.

"When we saw what the blockage was we were really shocked -- it wasn't something you expect to find in the sewerage network. Once we had cleared the blockage, the pollution stopped almost immediately. The team then set about doing a rigorous clean up operation to remove any visible signs of sewage debris or litter along the River Worth."

YW area manager Tim Williams described the incident as "an act of mindless vandalism".

He added: "Any unauthorised person who opens a manhole can only be doing so with the intent of causing mischief to the sewer system.

"We will continue with our investigations in Keighley and are also looking into any measures we can put in place to prevent this happening again.

"We are extremely disappointed and concerned about this or any pollution incident, as it goes against everything we work hard to achieve in the environment.

"Over the past few years our investment in the sewerage system and treatment works has led to a significant improvement in the quality of the region's rivers and watercourses, which has encouraged fish and wildlife to thrive."

The company says that while it makes every effort to ensure debris is not placed in the sewer network, with over 460,000 manholes throughout the county it cannot police every entry point.

It asks members of the public noticing any unauthorised person opening a manhole cover to report it as quickly as possible on 0845 1 242424.

Environment Agency spokesman Dave Preston said a member of the agency's fisheries department had gone out to the River Worth to assess the impact of the incident.

He added: "This is a tragic and unnecessary loss of life and it will take some time for the river to recover."

YW has pledged to re-stock the watercourse.