The chief target of their protest was Vancouver-based Eco Oro Minerals Corp.
The company is exploring for gold and silver in a high-altitude, environmentally sensitive area that is the main source of water for Bucaramanga's one million inhabitants.
This was the fourth anti-gold-mining demonstration in the area since 2010, and one of the biggest.
But Eco Oro shouldn't feel singled out. It is only one in a string of Canadian mining and exploration companies that have drawn the ire of local communities around the world.
On March 12, for example, more than 10,000 Greeks protested in Thessaloniki against several gold mining projects owned by Vancouver-based Eldorado Gold.
Then on March 21, Catholic priests marched with 5,000 locals in Matagalpa, Nicaragua, against a project owned by Vancouver-based B2Gold Corp.
Canadian companies have also been targeted in Ecuador, Peru, Bolivia, Dominican Republic, Slovakia, Romania and Israel.
"Canada is very well represented in global mining conflicts because, in large part, Canada is the home of most of the junior mining companies of the world," says Ramsey Hart, the Canada program co-ordinator at Mining Watch, an Ottawa-based advocacy group.
The reason for this, he says, is that Canada has a favourable environment for high-risk, speculative investments, the kind that drives international mineral exploration.
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Unlike the U.S. Alien Tort Statute, which allows foreign citizens to bring American companies to U.S. courts for abuses committed in a foreign country, there are no mechanisms to hold Canadian companies overseas accountable for their social and environmental policies. "We've just completely dropped that ball," Ramsey says.
The last attempt to impose minimum standards on Canadian companies was a bill sponsored by the opposition Liberals that would have set international standards for human rights and the environment for oil, gas and mining companies operating abroad, and would have made government political and financial support contingent on compliance.
Bill C-300, however, was defeated by six votes in a minority parliament two and a half years ago.
The people of Bucaramanga see the issue on their doorstep as a choice between water and gold.
They are worried that Eco Oro and two other multinational companies, AUX Colombia (part of the Brazilian EMX Group) and Leyhat (owned by Vancouver-based CB Gold Inc), will cause irreparable damage to the local ecosystem.
The high-altitude grasslands around Bucaramanga, known as paramos, lie above 3,000 metres in the tropical Andes, and Colombians are very protective of these ecosystems.
The paramos and Andean forests act as buffers that capture water during the rainy season, and then release it during the dry months.
Florentino Rodriguez, a spokesman for the Movimiento Cívico Conciencia Ciudadana (MCCC), a grassroots movement in Bucaramanga, says he recognizes the need for foreign mining investment in Colombia. But he also wants to see it conducted in a more disciplined way.
The main problem, he says, is that many mining titles in Colombia "overlap with strategic ecosystems, water sources, and important basins that supply municipal aqueducts" — Eco Oro being a case in point.
It's involvement in the Santurbán region around Bucaramanga goes back to the mid-1990s, when its predecessor, Greystar Resources, acquired numerous mining titles.
In 2010, the company proposed an open-pit project called Angostura, which sparked a backlash in the local community.
Faced by a rising tide of public opposition to the project, Eco Oro decided in 2011 to abandon the open-pit approach, not long before the Colombian environment ministry denied the company an environmental licence.
Eco Oro then shifted to an underground project, with the potential to extract an estimated 2.7 million ounces of gold.
A national park
For its part, Eco Oro says it has been a victim of misunderstandings and misinformation.
"We believe the people marching must take the steps to educate themselves about the impacts of mining in the region," says Fiona Grant Leydier, a Vancouver-based company spokeswoman.
The company insists that it wants to properly educate the people of Bucaramanga about the benefits that mining could bring to the region, and that it is working to the highest international standards to ensure long-term sustainability.
One of the obstacles is that the Santurbán paramo was declared a national park in late 2012.
In a statement in January, the company said: "The Angostura deposit, Eco Oro's principal asset, covers a total area of 215 hectares of which 193 hectares or 90 per cent falls outside of the surface boundaries of the (Santurbán) Park."
However, activists take the view that other nearby ecosystems, which are important for water retention, such as the lower-altitude sub-paramo and the high-Andean forest should also be included in the boundaries of the national park.
For now, Eco Oro still does not have an environmental permit for mineral extraction. However, it can continue with large-scale exploration activities, which do not require a licence.
That exploration is also raising concerns as the MCCC feels large exploration tunnels can reduce surface water.
Visits from the environmental authorities in 2012 found evidence of pollution and erosion caused by the exploration activities, according to a technical document from Colombia's National Environmental Licence Agency.
Environmental rules expected
It was the concern around the exploration that sparked this month's protest in Bucaramanga.
MCCC has also sent a letter to the Colombian Congress demanding that lawmakers take action against the exploration activities. Signatories included the former manager of the metropolitan aqueduct, engineers and academics from the most important universities of the region, a former mayor of Bucaramanga, and a former governor.
Gold mining in the region is not without its supporters, though.
The same day of the march in Bucaramanga, the local community near Santurbán, about 70 kilometres away, organized a counter-march.
An estimated 1,200 people from the region of Soto Norte took to the streets to defend mining operations for their contribution to the local economy.
Eco Oro, and its Canadian predecessor, had been operating in the area for more than 10 years. It expects that a new mine would employ around 1,000 people.
The Colombian government is currently preparing terms of reference for environmental licensing of large-scale underground mining.
Once these new rules are ready, Eco Oro will submit an environmental impact assessment for the Angostura project.
To further complicate the situation, the Colombian mining sector is in a legal void. In 2010 the government tried to replace the old, more environmentally permissive, mining code, which was the subject of controversy as it was developed abroad, in this case with the guidance of the Canadian International Development Agency (CIDA) in 2001.
But the new successor code was not created in consultation with indigenous populations so the constitutional court declared it invalid and gave Colombia's congress a two-year period to make a new one.
The deadline is May 11, and missing it will mean that the country will have to go back to the old code.
In the meantime exploration will continue, and so, likely, will the activists' struggle to protect their water.