‘No man ever steps in the same river twice”.

As I walk alongside the River Thames in Oxford watching the water surge past, this well-known saying from Greek philosopher Heraclitus often springs to mind. A trickling stream, the source of the River Thames, lies in a quiet field in the Cotswolds. As it flows through several counties, 20 or more tributaries, including the Windrush and the Evenlode, feed the river. Along its course the Thames splits into several small streams creating more than 80 islands.

In Oxford, you may be familiar with the Bullstake Stream, near the Botley Road, or the Castle Mill Stream in the city centre. This is still the Thames on its way to the tidal reaches in west London, through the capital to the Thames Barrier at Greenwich before flowing into the North Sea.

It is not only the water of the Thames that is constantly flowing. Everything that surrounds the river also changes.

In the past, the Thames would have been a broader and shallower river, meandering through wide beds of river gravels. After heavy rains, the water could spill over an extensive floodplain of marsh, reed bed and swamp.

Although many of these wetlands have been drained, and the river itself has been deepened and straightened, with market towns and cities now hugging the riverbanks, the Thames still supports an abundance of wildlife.

I live near the river, and every time I walk along the towpath the changing scenery and wildlife along the way offer me a fresh experience.

Last winter, the willows at Longbridges, near Donnington Bridge, were pollarded — the branches were cut off at head height to encourage the trees to regenerate and live longer. This is traditional management and for a few years lets more sunlight through to the riverbank allowing plants such as purple loosestrife and flag iris to flourish.

In some places, the towpath is artificially built up to provide a safe path for people to walk on when the river levels are high. Behind this barrier, water lies in pools creating areas of damp woodland and ponds. At Fiddler’s Elbow ,across the river from Sandford-on-Thames, ash and alder thrive with wet roots. I like hearing blackbirds and thrushes singing from the branches. Another tree found alongside waterways is the black poplar. Unfortunately it’s extremely rare in Britain, partly because of a virulent fungus called the poplar scab. It is a privilege to see the few remaining magnificent black poplars on the Binsey bank of the river at Port Meadow.

Over the last 18 years the River Thames has given me a lovely variety of experiences. I’ve canoed to Eynsham Lock and camped on a tiny island there. One hot summer I cleared overgrown vegetation from the Thames Path at Goring.

Each March, I join the OxClean team to clear up litter from the riverside paths. I’ll be at the Wildlife Trust’s Iffley Meadows reserve this April to count the thousands of snake’s-head fritillaries. I run, cycle and walk along Oxford’s towpaths beside the river almost daily. No matter how many times I do this, I feel that I’ve never stepped in the same river twice.

l If you would like to get involved in making spaces for wildlife beside the River Thames and elsewhere in Oxfordshire visit www.bbowt.org.uk or tel 01865 775476.