Demonstrators descended on Ottawa today to protest against a summit meeting between the leaders of Canada, Mexico and the US.

The main issues being discussed at the summit are water and potential exports to the US.

Since Canada first negotiated a free trade deal with the US in 1988, many in Canada have thought one thing about US motives: America wants Canada's water.

The often parched US south-west, the fastest growing part of that country, has a enormous thirst for water and Canada has a quarter of all the world's fresh water.

The summit does not even begin until tomorrow, but 5,000 people turned out in Ottawa to protest.

Concerns grew when a leading opposition politician accused Prime Minister Stephen Harper last week of having secret negotiations with the US over the export of Canadian water.