Betjeman's 'gentle Brent' and other urban rivers under threat from DIY plumbers

"Gentle Brent, I used to know you,

Wandering Wembley-wards at will,

Now what change your waters show you

In the meadowlands you fill!"

When John Betjeman, right, wrote those words about north London's river Brent, the poet laureate had Metroland, the suburban streets that had sprung up around it, in mind. He would never have imagined that more devastating changes would be wreaked on the river. But the Brent and countless other rivers in Britain have fallen victim to the cack-handed devotees of do-it-yourself plumbing.

More than a million DIY plumbing mistakes in homes across Britain have polluted our rivers with household waste. According to the Environment Agency, householders turned amateur plumbers are connecting dishwashers, washing machines, baths and even toilets to the wrong drains, causing waste to flow into rivers rather than sewage pipes. The results can be seen in rivers where grey sewage fungus is growing on the banks, filling the waters with substances that poison fish.

The EA blames the problem on the public's obsession with home improvements and soaring house prices, which can make it hard for people to buy bigger homes. Rather than take on a bigger mortgage, they opt to increase the size of their existing property by building an extension themselves, complete with extra bathroom and new kitchen. B&Q, the DIY giant, estimates that householders spend £150m a year on pipes, taps, sinks and baths.

What they often fail to realise is that in London's suburbs and in much of Britain, there are two sets of pipes – rainwater from gutters feeds directly into local rivers, via the drainage system, while foul household water travels through sewage pipes to sewage works.

Lucy Hannaford-Hill, field officer with the EA, which is responsible for preventing and cleaning up pollution said: "Householders don't seem to realise how much damage their ignorance can do to the rivers."

Among the worst-affected are tributaries of the Thames, which run through north and west London, including the Brent, the Crane and Mutton Brook. While the EA can do little but cut back the fungus, local councils can prosecute the amateur plumbers. Water companies can trace the source of pollution back through pipes and fines of up to £20,000 can be imposed on those responsible.

Ms Hannaford-Hill said: "One way of dealing with it would be to employ a plumber who understands the drainage system."

The Plumbing Institute, which represents professional plumbers, said it has asked the Government countless times to set up a registration scheme to stop cowboy plumbers getting work and making disastrous environmental mistakes.

Earlier this year, the EA said almost 87 per cent of urban rivers in England and Wales had good or fair water quality compared to 57 per cent in 1990. But, says Ms Hannaford-Hill, the DIY craze could undo all this progress.