Canals are man-made waterbodies that were once important for the transport of goods but nowadays are mainly used for recreation – both on the water and along the towpath.

Most suffer substantial pollution, exacerbated by the churning of motorised boats. A small number – like the Montgomery Canal – which still have clean and uncontaminated water, are outstanding freshwater habitats. And even where they do suffer pollution, tolerant and widespread creatures – like moorhen, mallard, roach and two-spotted water slaters – are able to use them as habitat.

There are two sides to every canal, literally. The towpath side, where horses once plodded along pulling the boats at a very leisurely walking place, is the more disturbed side and often banked with steel sheet piling for mooring up. The other side of every canal, known as the ‘offside’, is often inaccessible, frequently has more natural banks and may have tall emergent plants providing natural cover. These plants aren’t much affected by water pollution and grow healthily in the soupy water – they provide habitat for a range of birds – like the sedge warbler and occasionally the much less common Cetti’s Warbler.

Where are they found?

The canal network is about 2500km in length – which is in fact only a tiny proportion of network of freshwaters – around 1%. Most canals are in the lowlands, but they do snake around the uplands in some parts of the country.

What can you find living in a canal?

In the best and cleanest canals, a very wide range of freshwater plants and animals, including the most sensitive plants and creatures, are at home. Sadly only a tiny minority reach this standard – and these are wonderful biological refuges. Canals are not quite like any other freshwater habitats – people often say they are like long ponds, but because they are quite deep, narrow and gently flowing, they are more like the deep, sluggish and rich rivers that would once have coursed across lowland floodplains before land drainage engineering took hold. Being permanent, they support fish, so have those plants and animals that are happy to co-exist with fish – maybe 50% of all freshwater creatures.

Why are they important?

The best canals are true wildlife jewels but the overwhelming majority are polluted – some 95% of the canal length – and to the freshwater wildlife lover some of the most depressing places to visit. All but a few suffer the twin impacts of pollution and, on the well-used and popular canals, the regular to-ing and fro-ing of boats which churn up sediments and leave the water brown, muddy and turbid. These canals are not particularly important for their underwater wildlife. But for animals that live on or near water and aren’t too fussed about pollution, canals can be great. Often the best bits are the tunnels and bridges, which can be really important bat habitats, and where there aren’t any mink and the banks are well-vegetated, water voles use canals too. The commoner coarse fish are present, and where there are fish you will naturally see the occasional kingfisher or heron, and nowadays a visiting otter. None of the organisms depend on the canals – they are generalists that use what the canals provide.

What we’re doing to help

We developed 15 years ago the national monitoring method for assessing the biological condition of canals – called Canal PSYM. This can help people assess whether the condition of their canals is getting better or worse. But we’ll mainly be highlighting the need to protect the most important canals biologically – the irreplaceable waters like the Basingstoke Canal in southern England and the Montgomery Canal on the border of England and Wales. These are both canals with exceptional water quality – for these to maintain their quality, vigilance will be needed.

We won’t be popular for saying it, but often the best thing to do will be to make some clean ponds alongside the canal, rather than trying to do the impossible or unnecessary, like reducing boat traffic. After all, canals are mainly for boats.