BRITAIN's rivers are markedly cleaner than they were even at the beginning of the decade. Streams in Bradford may still smell like open sewers and the Mersey may be heavily polluted with mercury, but headway is being made against the filth. That was the limited good news yesterday from the National Rivers Authority, which regulates water quality.

Consumers can now feel a little better about recent huge increases in their bills, which have been required to finance fresh investment by the privatised water companies. They can take comfort from the knowledge that extra spending on treatment plants and piping is not just money down the drain.

Such news might be expected to encourage further expenditure on improving the country's water courses. Yet the danger is that the small advances reported by the NRA will not be built upon. There is still no system of making polluters pay for the damage they do. Big fines are meted out to the worst offenders, who are often expected to finance clean-up operations. But the charge for a licence to discharge bears no direct relationship to the impact of the effluent on the environment. An over-indulgent attitude to dirty industries is costing the countryside dearly.

Ministers also seem reluctant to back further costly improvements beyond those required by European Union directives. So the billions spent on investment in the next few years is likely to be concentrated on cleaning up coastal bathing waters and making drinking water even purer than it already is. Against these priorities, the cleansing of Britain's rivers is in danger of coming a poor third.

Such a policy would be understandable. We do not drink from rivers, and only the courageous or foolhardy swim in them. As long as the stink is not too unbearable or a danger to health, there are arguably better ways of spending money than on reducing pollution. But that would be to suggest that the value of rivers lies only in their usefulness. Waterways have an inherent beauty which is worth preserving. Anglers are not alone, for example, in feeling horrified to see the Wharfe, which sparkles through the Yorkshire Dales, become a murky, foul waterway once it joins the Ouse.

Clearing up this mess will cost money. The National Rivers Authority calculates that a serious programme of river improvement will cost pounds 918m over five years. That sounds like a lot on top of the billions of pounds required by European directives. Yet it amounts to a mere pounds 3 extra a year on the average domestic water bill. This would be a small price to pay for restoring Britain's rivers to a decent standard. It is an increase that Ofwat, the water industry's economic regulator, should sanction when announcing future price limits in July.

If the price is too high for the poorest consumers, the Government should devise a way of cushioning the blow for them. It might start by introducing a system that makes the polluters pay.