One of the world’s largest gold mining operations is about to open in the Dominican Republic, where the industry has a toxic legacy of pollution that stained rivers a searing red and failed to lift the fortunes of this largely poor country.

Abandoned 13 years ago by state-owned Rosario Dominicana, the Pueblo Viejo mine left behind an environmental mess and a cluster of depressed mountain towns.

Now, a joint venture by the world’s two biggest gold companies, both of them Canadian, is launching a much larger operation at the site within weeks. Officials promise it will be radically different from the previous one, and will be managed to prevent environmental damage, in addition to underwriting the cleanup of past contamination and providing billions of dollars for the country, especially in the mining region in the forested mountains north of the capital.

But skeptics are uneasy about the cyanide used to process the ore and question whether the operators can guarantee their assurances to contain chemical runoff in a country prone to major flooding, especially during hurricanes.

“We are not against mining in the Dominican Republic necessarily, but the industry has been its own worst enemy here,’’ said Luis Carvajal, a biologist at the University of Santo Domingo and a prominent critic. “Without a doubt, the impact of the mine will be significant.’’

Pueblo Viejo Dominicana Corp. has waged an extensive campaign to defend itself, acknowledging the past problems that mining has caused in the country but otherwise dismissing what it says are largely unfounded fears.

“People have been scared, people have actually had a bad experience and now it’s up to us to prove we can actually do the contrary,’’ said Manuel Bonilla, president of the joint venture, which is 60 percent owned by the Barrick Gold Corp. of Toronto and 40 percent by Goldcorp Inc. of Vancouver.