Enter the Colombian military, which is building a US-financed coast guard station on Gorgona Island, and a spat erupts -- one that is challenging Colombia's new leftist president, Gustavo Petro, to make good on promises to fight climate change and be an environmental champion.

Environmental groups filed a class action lawsuit last month asking a judge to suspend construction of the base, which the navy says will help it fight drug trafficking and other crime.

"But even better would be for Dr Petro to fulfill the promises he made as a candidate," said Jorge Robledo, a former senator serving as spokesman for the conservation groups who filed the suit.

"If the president, who is commander in chief of the armed forces, wants to end this project he can do it in a second," said Robledo.

He said Petro, who took office in August, has to fulfill the ambitious conservation and climate change program he campaigned on.

The navy says the coast guard base will give it a tactical advantage in fighting drug trafficking and environmental crimes like poaching.

"If the project is not carried out, the ones who come out winning are the criminals," coast guard commander Javier Bermudez told AFP.

Gorgona -- the name comes from the snake-haired gorgons of Greek mythology -- is situated in a maritime corridor used to smuggle drugs northward.

Bermudez said three environmental impact studies have been done to assess the risk posed by the base.

-Fragile ecosystem -

Some say the protected nature reserve set up on and around Gorgona Island is as rich in biodiversity as the Galapagos islands off the coast of Ecuador.

Colombians know it for a darker reason, however: it used to house a prison where prisoners deemed to be the most dangerous were sent and tortured. That facility operated from the 1960s until 1984.

These days the island 60 kilometers (40 miles) off the southwestern coast of Colombia is better known for its tourists, who are lured by its coral reefs, exotic fauna and thick forests.

Felipe Guhl, a biologist at the University of the Andes, said the base construction work will surely harm the island, which is only 11 kilometers long and four kilometers wide.

He called Gorgona a fragile biological sanctuary where any kind of human intervention will hurt the coral reefs, fish and animals.

In 2015 the government agency that grants environmental certification approved construction of the base, which will feature a 132 meter dock, a radar installation and housing for military personnel.

The project is receiving financing from the United States, which is the main partner of Colombia -- the world's top cocaine producer -- in fighting drug trafficking.

The navy says that in waters near the island a variety of crimes are committed in addition to drug smuggling: contraband, illegal fishing, deforestation, poaching, sea pollution and others.

"Why build a base on the island when it could just as well be on the coast?" Guhl asked. "A 60-kilometer distance from the island to land should not make much of a distance what with the technology that we have today" when it comes to surveillance, he said.

- 'Environmental authority' -

Some 6,400 tourists visit the island every year, and have to make an awkward disembarkation because it has no dock at present, said Daniel Agudelo, who runs the nature parks on Gorgona and says the base project is feasible.

Commander Bermudez of the coast guard said the base is needed to fight crime.

"We cannot have protected areas made out of paper. We need the work of police to exercise that environmental authority," he said.

But Guhl said the project must be halted because "from a biological standpoint, Gorgona Island is a treasure."