The extent of water pollution in Britain is shocking: clean water is almost non-existent, and life in freshwater is under constant threat. Away from the mountains and moors, in an average part of the countryside, most of the freshwater in that landscape will be polluted to a degree that damages the life in that water. At a national level, only a quarter of streams, rivers and lakes meet the minimum legal standard. Most ponds are in poor condition too, which matters because in most parts of the countryside they support the widest variety of freshwater life, more than either lakes or rivers.

To counter the poor condition of our freshwater, wildlife charity Pond Conservation recently announced that it has teamed up with the Game & Wildlife Conservation Trust in a groundbreaking, million-pound research project to discover why our rivers and ponds remain so polluted. The project, called Water Friendly Farming, was set up in response to the failure of measures designed to protect our watercourses.

Though otters have returned to most parts of the country they are one of the few success stories. Nationally, salmon are at an all-time low, native crayfish are gone from most of the South, nutrient-sensitive water plants ? a vital part of any freshwater system ? are in retreat more or less everywhere and some species are on the verge of disappearing. Only last month, the largest population of pearl mussels in England was virtually wiped out by low river flows in the Lake District. The equally endangered glutinous snail ? a medium-sized pond snail that needs the cleanest water ? is now extinct in England, holding on in one lake in Wales. Almost everywhere the species surviving are the tough and unfussy plants and animals ? while the rest seem to be dwindling away.

For creatures and plants that spend all their lives in or under water, the effects of pollution are clear, but it?s harder to pin down exactly how pollution is affecting quarry species. The availability of ponds, lakes and wetlands for duck is vital and mallard and tufted duck have increased over the past 40 years, probably in part because of the post-war increase in lakes made by gravel digging. Though wintering mallard numbers are steadily declining, this is most likely to be due to changed weather patterns. But there?s no doubt that on individual ponds and lakes, an abundance of water plants ? both around the water and below the surface ? is beneficial for dabbling and diving ducks. Where submerged waterplants are lacking, it?s likely to be bad news for waterfowl, and pollution kills waterplants.

The pollutants

When we talk about water pollution, because there are so many sources, it?s simpler to ask where the pollution isn?t coming from. Unpolluted water exists in land where there is more or less natural vegetation such as heathland, and forests where we aren?t using biocides, fertilisers, cultivating the land for crops or leaving it bare so that soils can wash away.

If a river system drains towns, villages, roads or most modern conventionally farmed land, it will be polluted. Added to this are the countless sewage works that discharge treated effluent into rivers and streams. This dirty water is cleaned up a lot more than in the past ? but it?s far from clean. And living out in the country is no guarantee your local stream will be immune from this: there are thousands of septic tanks intercepting the toilets from rural houses and businesses that run into the nearest small stream.

However, there is no doubt that a large part of the threat to life in freshwater comes from the way we farm the land. In grassland farming, especially dairy, the fertilising of fields and management of animal manure are the main problems. Here the pollution can be as bad as from sewage works. In arable areas, sediment, fertilisers and sometimes biocides are the main issues. But it?s not just the fields: rural roads can be a significant source of pollution, too. These problems are all well-recognised and there is a huge amount of research going on to find out how to stop the damage.

Are things getting better?

In Britain, we have reliable monitoring of rivers only from the late-1980s and early-1990s. A few big lakes, such as Windermere, have been monitored for 60 or 70 years but we have virtually no long-term monitoring of ponds, even though these are one of the most abundant freshwater habitats. This monitoring shows that, since the 1990s, there have been modest improvements in rivers. Lakes and ponds, on the other hand, have probably never been worse.

Looking further back, before the 1970s, is more difficult because we don?t have the data. Compared with immediately after World War II, when sewage works were discharging poorly treated effluents and heavy industry was still heavy, the most polluted rivers have improved substantially. At the same time, so-called diffuse pollution ? coming from farmland and residential areas ? may now be higher than ever. For example, in the Thames just upstream of London, nitrate pollution levels are at their highest for more than 150 years. This probably means that more or less every little stream, river and lake in the UK has the highest nitrogen levels ever.

Controlling diffuse pollution

Dozens of different methods for controlling diffuse pollution from farmland have been proposed. Because of this we spend millions of pounds on schemes to put in buffer strips, fencing cattle out of streams, controlling the use of fertilisers and putting bends back into rivers. The question is: Is it working?

So far, the evidence shows that our measures to protect freshwater aren?t living up to the hype. The effectiveness of different methods ? the buffer strips and stream fencing ? is more variable than we originally expected.

Often the application of these measures is too piecemeal across the landscape: unless you make sure all the fields are buffered it?s not going to make a difference. And often these measures are just not applied well enough. For example, there?s little gain if a buffer strip is simply bypassed by a field drain running underneath it, which happens in very many cases.