Project

The dam project

Last updated:: 12 January 2026

View of the Pantheon and lake in October at Stourhead, Wiltshire with autumnal trees in the foreground and a blue sky with clouds — View of the Pantheon and lake in October at Stourhead, Wiltshire | © National Trust Images/Mike Calnan

Created as part of the vision of Henry Hoare ‘The Magnificent’, the man-made lake at Stourhead is over 250 years old. Like anything of that age, it often needs conservation work. The dam that holds the water in the lake is currently leaking and needs repairs.

The lake at Stourhead

Created as part of the vision of Henry Hoare ‘The Magnificent’, the man-made lake completes ‘Paradise Valley’, and is what makes the landscape garden so unique.

Like anything of that age, the lake often needs conservation work. The dam that holds the water in the lake is currently leaking; the water level is very slowly going down.

Following our mission to conserve the places we look after, the National Trust has begun a project to repair the dam.

The nature of the repair work means that a small section of the lake walk by the dam is closed to visitors. However, the great majority of the pathways around the lake are still open and the views are still as wonderful as ever.

We hope you enjoy seeing this vital conservation work in action as we maintain this beautiful lake for centuries to come.

The dam project timeline

12 January 2026

Contractors arrive

Specialist contractors arrive and set up their site compound, ready for works to start later in the week.

We are sharing two new walking routes with visitors as a full circuit of the lake is not possible whilst the work to the dam takes place.

The Aeneas’s walk takes in the Temple of Flora, Grotto and Pantheon as you explore classical inspiration behind the garden.

Apollo’s walk takes in views across the lake and from the vantage point of the magnificent Temple of Apollo, ancient sun god.

Repairing the dam today

The lake is classed as a Category A reservoir – the highest possible categorisation for environmental risk management. Although built over 250 years ago without any of the equipment or building techniques we would recognise today, the lake is still subject to regular monitoring and specific flood test legislation.

The dam is under constant pressure. A large body of water is incredibly heavy, and a dam needs to be extremely strong to withstand that weight of pressure. It is essential that a leaking dam is repaired; under the pressure of a large body of water a small leak can quickly become a big one, potentially leading to a disastrous burst.

Isolated leaks were detected in the dam in 2022 and repaired, but continued surveying has shown the dam has an increasing tendency to allow water through the embankment wall. The only option now, to avoid decreasing water levels and continued wear and tear on the dam is to undertake essential repair work.

The dam was made using the waterproof gault clay that happily forms part of Stourhead’s natural geology. It is this amazing feat of Georgian engineering that we are repairing, so that the lake stops leaking and continues reflecting the natural beauty of Stourhead.

It’s not the first-time repairs have been made to the dam. Among many additions and repairs to the lake over the centuries, a new water wheel was installed in 1907, and the dam was extensively restored between 1918–1920, with further work carried out in 1945.

The repair work we are doing today is the latest in a long history of maintenance needed by a large, complex dam like this one.

key facts

c.178,000m3

The volume of water in the lake. Over 70 Olympic sized swimming pools.

2 years and 12 labourers

It took two years for the dam to be built by 12 labourers who were employed in banging down the layers of clay to form a watertight bond.

220m wide and 10m tall

The dam spans 220m and stands at 10m tall from the bed of the lake.

Lake facts

At 18 acres, the lake takes up around a quarter of the formal landscaped area. It is essential that we repair the current leak in the dam at the western end and continue to conserve this beautiful landscape for future generations.

At 300m long and up to 10m high, the dam was a considerable feat of Georgian engineering. If a dam bursts it can cause huge damage, so the water level, flow and pressure need to be managed carefully.

The original engineers in the 18th century installed a series of drains, sluices and spillways to minimise stress on the dam structure, and to manage the water flow and keep a constant level of water in the lake so that when the level is low, water can be conserved in the lake. When it’s too high, water can be let out to the pools below.