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Rideau Canal

Ottawa, Canada




5 years


£822, 804 (£85m today)


Project achievements

Economy boosted

Leisure boats use the waterway, and the areas along its route are boosted by tourism

Solved the problem

Create a trade route connecting Ottawa to Ontario

Used engineering skill

Build a canal using a slack water system

Construct a canal to connect Canada's capital Ottawa to the St Lawrence river in Ontario

The Rideau Canal – also known as the Rideau Waterway – connects Ottawa, the capital city of Canada, to Lake Ontario and the St Lawrence river at Kingston, Ontario.

At 202km long, the structure has 47 locks and 52 dams. The route uses parts of the Rideau and Cataraqui rivers, as well as several lakes. Opening in 1832, the scheme is the oldest, continuously-operated canal system in North America.

The canal was built amid reports that the United States had intended to invade what was then the British colony of Upper Canada during the War of 1812 – a conflict between the US and Britain that lasted from 1812 to 1815. The British built several canals – as well as forts – to deter future American invasions.

Although the canal was initially a military project, it was also used for trade, as it was easier to navigate than the St Lawrence River. The St Lawrence had a series of rapids between Montreal and Kingston.

The scheme was designed and supervised by London-born Lieutenant-Colonel John By of the Royal Engineers, using a ‘slack water’ system.

A slack water system meant engineers built dams to drown rapids along the route, rather than cutting a canal around those rapids. This made the canal easier – and less expensive – to build.

The scheme was designated a National Historic Site of Canada in 1925 and made a United Nations World Heritage Site in 2007.

Rideau Canal

Enda Casey talks to us about Rideau Canal.

Did you know …

  1. The canal went considerably over budget. John By was recalled to London and made the scapegoat for the extra costs – accused of making unauthorised payments from government cash.

  2. Although a parliamentary committee cleared him of any wrongdoing, By was forced to retire from the Royal Engineers with no acknowledgement for his work on the scheme.

  3. John By is still remembered in Canada for building the Rideau Canal. Apart from a statue and other memorials, a building at the University of Ottawa is named after him. A stamp was issued in 1979 to mark the bicentenary of his birth.

  4. The canal freezes over during the winter, and the 7.8km-long Rideau Canal Skateway holds the Guinness World Record as the world’s largest naturally frozen ice rink.

Difference the project has made

Although the canal was never used for military purposes – hostilities with the United States were over by the time it was completed – it became an important route for trade across the country, carrying timber, minerals and grain to Montreal.

Thousands of immigrants arriving in Canada from Britain in the late 1840s used the canal to travel to their new homes.

The scheme is now mainly used by leisure boats and tourists – bringing income to areas along the route of the structure.

How the work was done

The Rideau Canal is an example of adaptive engineering. Almost all of John By’s original plans – based on surveys of the route – had to be changed to deal with conditions the project team encountered building the scheme.

John By intended the canal’s dams to be overflow dams – a structure that allows water to flow over the top when water levels are high.

Spring floods during construction convinced By that he’d need weirs at every lock instead. A weir is a barrier that raises water levels upstream - they’re used to prevent flooding.

Engineers also had to change their plans when a stone arch dam was washed away three times during building work. They replaced the structure with a stone-filled timber crib dam.

A timber crib dam is made of heavy lengths of timber, fitted together in a similar way to a log house. With an interior filled with rocks, the heavy crib structure supports the face of the dam and the weight of water pressing against it.

Although accidental deaths were relatively low for such a major project, around 1,000 workers died from disease – mainly malaria. Memorials to the dead have since been erected on the canal route.

People who made it happen

  • Client: the British government
  • Designer: Lieutenant-Colonel John By

The canal was excavated and built by thousands of Irish and French-Canadian workers.

More about this project