How Deep Is the River Thames Running Through London?

The River Thames cuts its course through London proudly, claiming a large portion of Britain’s history. If not for this 215-mile-long riverway, England would not look the same as it does now. The significance of this river is vast, and the history of it is long. Over 200 bridges cross this great river, and commerce historically relied on it. Today, we’ll explore some of that history and also answer one important question – how deep is the River Thames? We’ll take a look at its average, minimum, and maximum depths as we wind our way down the river toward the sea.

Where Does the River Thames Begin?

The River Thames begins in the county of Gloucestershire. The Thames Head is a spring called Lyd Well and it rests in a Cotswold meadow. Jurassic limestone defines the Cotswolds region and influences the grassland habitat that springs up and spreads across the rolling hills and prairies of the region. This is a rare habitat for the United Kingdom, full of farmland and Cotswold stones. A series of meadows decorate the landscape in this central southeastern region. Officials designated this region as an “Area of Outstanding Natural Beauty” in 1966. Trewsbury Mead, the meadow from which the Thames springs, is 3 miles southwest of Cirencester. We’ve included a map of where the River Thames begins.

It is important to note that the Thames Head is a series of springs. Due to changes in climate and loss of rainfall, the source of the river varies from spring to spring. The listed source of the Thames has changed as of August 2022 and now rests 5 miles downstream of Lyd Well. This newly designated source, Somerford Keynes is currently a temporary shift from Lyd Well. If the region doesn’t see significant rainfall in the coming years, Somerford Keynes may become the new permanent source for the River Thames. Visitors to the area can still see the original source by following a footpath across Trewsbury Meadow. This is an easy walk and will lead you to a ring of stones that surrounds the source spring. You won’t see much water when you visit – most of the year the meadow reveals only a dry, shallow riverbed.

From this region, the River Thames flows eastward.

The Course of the River Thames

The river continues to flow in an eastward direction when it leaves its headwaters. It flows through several counties, including Oxfordshire and Buckinghamshire. Several important cities rest along its banks as it flows toward London. Visit Reading, Windsor, and Hampton to catch a glimpse of the river as it makes its way to the sea. The river flows through the center of London and continues past Greenwich and Woolwich.

A few miles upstream from London, in Teddington, the Thames becomes tidal. A tidal river is a river whose flow and level are a direct result of tides. This also means that all of the river water from the Thames in London is brackish – a mixture of fresh and saltwater. The Tideway is the portion of the river Thames that is tidal and brackish. It accounts for 95 miles of the river, providing important estuary habitats between London and the North Sea.

The river flows in a dominantly easterly direction over its entire 215-mile course. It does spend some time curving north or south, but always rights itself to flow east. The river has several tributaries along the way. We’ve included a table of the main tributaries below.

The Mouth of the River Thames

After several miles of tidal, brackish estuary, the Thames opens up to meet the North Sea. The main portion of the estuary is right at the mouth of the River Thames, with the city of Southend-on-Sea to the north and the city of Sheerness to the south. There is a large sandbank that marks the mouth of the Thames Estuary. This sandbank, “The Nome”, marks the end of the estuary and the beginning of the North Sea.

Significance of the River

The River Thames is the largest river in England and the second-largest in all of the United Kingdom. It is only shorter than the River Severn. A river this large definitely bears significance. It has historically been used as a critical trade route. It also served to separate social classes for a long time. A lot of the impoverished neighborhoods rested south of the river while the posh ones sat to the north. Several pop culture references allude to this, but today’s London looks a lot different than the London of the past. Now, you can find affordable eats and digs on either side of the river, with posh neighborhoods like Wimbledon to the south and Chelsea to the north.

London’s position actually relies completely on the River Thames. Let’s explain that further. Did you know the Romans built London? The early London area was a small and predominately Roman town. The Romans built this town on the banks of the Thames for several reasons, most of them strategic. They found a span of the Thames close to the sea that was still narrow enough to build a bridge over. This is a similar strategy to the construction of Rome, itself. Next, the portion of the river they settled was still close to the North Sea and, so following, access to the rest of Europe. The strategic location picked by the Romans continues to serve London to this day. Trade and commerce on the Thames were integral to the growth of London.

Now, there is a vast amount of recreation that takes place in and around the waters. Dragon Boat Racing is a popular sport and even has a yearly festival in London. There are several other boat festivals that take place in London and draw happy crowds. Commerce is still an integral part of the River Thames experience, as well. Over 5 million tonnes of goods reach their destinations via the River Thames yearly. This reduces commercial traffic on England’s roads significantly – over 200,000 lorries (semi-trucks) are kept off the highway because of the river’s use as a commercial shipping channel.

How Deep is the River Thames in London?

The River Thames reaches a maximum depth of 66 feet, making it the deepest river in the United Kingdom. This is in contrast to the average depth of the river – 10-20 feet. The river varies so much in average depth because of its tidal region. Almost half of the river is tidal, which causes some water levels to rise and fall dramatically with daily and seasonal tides. The river also gets quite shallow in some areas. Under London Bridge, it is less than 5 feet deep. Its widest portion is near its mouth and spans about 18 miles. It narrows to as little as 59 feet wide near Lechlade. That’s still quite a wide river!

You can find the deepest part of the River Thames in the estuary region east of London. The average depth of the river, as it flows through London proper, is less than 15 feet.

Quick Facts About the River Thames

• The River Thames is very old and dates back to the Jurassic Period (140-170 million years ago!).
• This river smelled so bad in the 1800s that it got the nickname “The Big Stink”. At one point, Parliament closed due to the stench.
• Tidal flooding plagued the cities – especially London – along the tidal portion of the river. This resulted in the construction of the world’s largest moveable flood barrier – the Thames Barrier. However, the rising sea levels from climate change may render this flood barrier useless.
• The river was declared biologically dead in the 1960s, meaning that it was so polluted that life couldn’t exist (compare this to the dead zone in the Gulf of Mexico).
• You can functionally swim the full length of the River Thames, but the Port of London Authority restricts swimming through most of its jurisdiction.
• The river used to freeze in London. This event hasn’t occurred since the 1800s.
• The river provides 2/3 of London’s drinking water.
• Over 50 people die every year in the River Thames.
• There are sharks in the river! The venomous Spurdog swims in its waters along with its nonvenomous relatives, the tope shark and the starry smoothhound.
• A 5,000-year-old human bone was found in the river in 2022.
• A walking trail follows nearly the entire course of the river.

The photo featured at the top of this post is © steve estvanik/Shutterstock.com