Organized crime cartels have turned to Costa Rica's treasured nature reserves as governments wage military offensives against the gangs throughout Mexico and Central America.

In the mangrove swamps and jungles, the traffickers have found a vast, sparsely populated and thinly policed paradise that they can use as a stop-off point on their way to smuggle Colombian cocaine to the United States. They also increasingly grow marijuana amid the cedar and lemonwood trees.

Costa Rica prides itself on not having a standing army but the incursion has put lightly armed park rangers into the frontline of the drug war as they struggle to prevent hikers and swimmers bumping into any rude surprises.

In January, the Coast Guard was called in for an unprecedented seizure of almost 1 ton of cocaine found in swampy mud in the Palo Seco park. The drugs would have been worth about $100 million on the U.S. streets.

In total, Costa Rican authorities seized more than 6.6 tons of cocaine in the first half of this year both in and out of parks, compared to less than 3 tons in the same period last year. In all of last year, 8.9 tons of cocaine was seized.

Park rangers have also uncovered dozens of gangster encampments, complete with food supplies.

"Drug traffickers come in, make new pathways into the park for their trucks and set up their camps, waiting for drug shipments to come in by boat," said Carlos Martinez, head of police in Quepos, a town near Costa Rica's most popular park Manuel Antonio, 80 miles (130 km) from the capital of San Jose.

"We've found gasoline containers, remains of water and food supplies and canvas used to cover up the drugs. They've even made themselves some benches to sit down and chat."

BALLOON EFFECT

Drug cartel expansion into Costa Rican parks is seen as part of a 'balloon' effect of the narcotics trade, which has been attacked by military offensives in Mexico, Colombia, Honduras and Guatemala.

"You squeeze the balloon in the south, then you squeeze it at the top and what you get is pressure in the center, so even if it's not the capos themselves that are moving down here, the cartels' operations are extending to Central America," Costa Rica's anti-drug czar Mauricio Boraschi said.

Police say the smuggling is carried out mainly by Mexican cartels, including the Sinaloa Cartel, La Familia and the Gulf Cartel. Last month, Costa Rican police arrested the alleged head of the Gulf Cartel's operations in all Central America, Juan Manuel Garcia, in San Jose.

Traffickers bring large amounts of cocaine out of Colombia's Pacific port of Buenaventura from where they can sail straight into parks like Manuel Antonio, which has large stretches of Pacific beach, Boraschi says.

They can then continue their route north on the Pan-American Highway, or organize further trips up the Pacific coast.

Costa Rica abolished its army in 1948, a move that is celebrated annually, so the Central American nation is unable to pursue a Mexican or Colombian-style military crackdown.

However, the Costa Rican government has strengthened cooperation with the United States Navy in hitting traffickers in the South Pacific.

It also recently levied a special tax on businesses to raise $70 million for anti-drug efforts, including special police units.

U.S. Drug Enforcement Administration spokesman Michael Rothermund said local DEA agents worked closely with Costa Rica's judicial and drug control police.

"Costa Rica has been a good partner in this fight", said Eric Nelson, deputy ambassador to the United States in Costa Rica. "We think they're making good decisions like increasing their security budget and combating corruption."

The incursion of the drug trade has yet to cause a spike in violence as traffickers try to stay off officials' radar, forgoing the attacks on security forces seen in Mexico.

Costa Rica's homicide rate fell for the first time in six years in 2011 to 11.5 murders for every 100,000 inhabitants, bucking a trend of increasing violence in Central America.

Honduras, which holds the title of murder capital of the world, had a rate of 86 per 100,000 last year.

LONE RANGERS

The cartels have not attacked national park rangers but there is increasing concern about the safety of travelling to distant corners of the reserves.

"Their duties used to be mainly conservation, environmental education and looking after park visitors", says Rafael Gutierrez, head of park rangers at the government's National Conservation Areas System. "Now their job has changed."

Costa Rica's 28 parks cover a quarter of the national territory of 1.5 million acres, meaning there are almost endless marshes, mountains and jungles where traffickers can hide.

To pull out the ton of cocaine in Palo Seco in January, officers spent an entire day fighting through swamp water that went up to their necks, battling mangroves and swinging roots.

Costa Rica is particularly keen to control the gang's incursions as the parks are a major draw for tourists, with some 300,000 visitors annually. Tourism generates some $2.1 billion a year, roughly 5 percent of gross domestic product.

"It's such a shame that this has to happen", said James Kaiser, an American writing a travel guide about Costa Rica. "But as someone who visits national parks I don't have any reservations about visiting the most popular parts of the parks because I think those are not the areas that the drug traffickers are going to use."

Police officer Martinez agreed that tourists were highly unlikely to bump into cocaine smugglers but said they were keeping an extra eye out for wandering visitors to make sure that did not happen.

"The biggest danger is that there is a confrontation between the narcos and a tourist," police officer Martinez said.

"We're always looking for the adventurous surfer who could get lost looking around for the perfect wave." (Editing by Ioan Grillo and Krista Hughes)

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