The U.N. Industrial Development Organization has identified Colombia as one of the world's biggest per capita polluters of mercury, used in artisanal mining, mining opponents say.
"Development, foreign investment, the generation of jobs or promises for improved living conditions for locals cannot be used as arguments to jeopardize the water wealth of our paramos (highland moors)," the country's national retailers association, FENALCO, said in a statement.
The association is opposing the Angostura open pit mining project expected to produce gold and silver over the next 15 years, run by Canadian company GreyStar in the northern province of Santander.
"We do not support this activity, which will cause irreparable and irreversible damages," Erwing Rodriguez, director of FENALCO in Bucaramanga, the provincial capital, told Inter Press Service.
GreyStar denies the mine will damage the environment.
Other groups have joined FENALCO in its opposition to the mine.
"It's exciting that for the first time, a conglomeration of groups and people, including the upper-middle class, social organizations, leftist political groups and environmentalists, have come together around one goal: protecting our water," geologist Julio Fierro said.