Crime and joblessness have long been part of the tough Leon XIII neighborhood of Costa Rica's capital, where residents such as Alexandra Martinez do their best to steer clear of broken pavement and street-corner drug dealers.
But the 37-year-old homemaker says that things have gotten worse in the last few years. Her explanation: "There are a lot of Nicas here," she says, using a slang term for Nicaraguans.
Martinez says these immigrants, many of them undocumented, are hard-drinking, aggressive people who compete with Costa Ricans for jobs and drain the nation's public services. She approves of a recent federal law aimed at stemming the influx.
"It's the biggest problem we face in the country," she says.
Many Costa Ricans are more temperate than Martinez when discussing immigration. But the continued southward flow of impoverished Nicaraguans into Central America's most prosperous nation has inflamed tensions between these neighbors.
The 192-mile border is virtually unguarded, allowing Nicaraguans to slip easily into Costa Rica, where the per capita gross national income of $4,700 is six times higher than in Nicaragua.
Some analysts say Costa Rica, known as the Switzerland of Central America, has benefited from the steady supply of cheap labor to harvest the nation's bananas and coffee, mop its floors and tend to its children.
Costa Rica boasts the region's highest standard of living and provides universal healthcare. The nation has invested heavily in education and boasts a thriving technology industry.
But nagging poverty, sluggish economic growth and fraying of the social safety net have many Costa Ricans fearful that uncontrolled immigration is undermining their hard-won gains.
An estimated 180,000 undocumented Nicaraguans account for about 4.5% of the nation's population, a slightly higher percentage than the overall proportion in the United States, where illegal immigrants make up 4% of the population.
Including legal residents, experts calculate that as much as 15% of Costa Rica's population is foreign-born. Most of them are Nicaraguans, who have been arriving in large numbers for 25 years because of war, natural disasters and social instability in their country.
"Even the United States would have problems" absorbing so many newcomers, says economist Eduardo Lizano, president of the San Jose think tank Academy of Central America.
Approved late last year and slated to be implemented in August, Costa Rica's new immigration law is aimed largely at those who profit from undocumented workers. It makes human trafficking a crime punishable by as much as six years in prison. And it significantly increases fines on Costa Ricans caught employing illegal immigrants -- to $3,600 per violation, up from as little as $10, says Johnny Marin, Costa Rica's immigration director.
Marin says the nation of slightly more than 4 million people lacks the resources to guard its border or to engage in mass deportations. Costa Rica deported just 775 people last year.
"Control of the migratory phenomenon lies in the employer sector," Marin says. "Because if they don't hire illegals, the people won't come, they won't migrate."
Marin says immigration has largely been a good thing, providing Costa Rica with labor and cultural diversity. But he says rising acrimony has necessitated reforms.
Costa Ricans blame Nicaraguans and other foreigners for all manner of ills, Marin says. News reports frequently note the nationalities of foreigners accused of crimes, particularly Nicaraguans and Colombians.
He cites an urban myth here that 1 million Nicaraguans are living in Costa Rica.
"The theme of migration awakens passions here," Marin says. "Migratory chaos is always dangerous.... We have to maintain an equilibrium."
Some Nicaraguans living in Costa Rica say their lives have become more difficult because of increasing resentment. Juana Lopez recounts how a security guard humiliated her and her children at a public park.
"The guard asked me for my identification card and documents for my children, and he wouldn't let me in. He said we don't have the right to enter any playground," says Lopez, who lives in a San Jose slum known as Triangulo Solidario, a tangle of tin and wood shacks.
The immigration issue has added to long-running tensions between Costa Rica and its northern neighbor. The countries are embroiled in a dispute over navigation rights to the San Juan River, which runs between them. Nicaragua recalled its ambassador to Costa Rica last fall and previously sent troops to the border region, a move viewed as particularly provocative by Costa Rica, which has no standing army.
Nicaraguans are incensed by the November death of Natividad Canda Mairena, a Nicaraguan living in Costa Rica. A suspected burglar, Canda was mauled by a Rottweiler guard dog for 1 1/2 hours while bystanders watched. The attack prompted a barrage of jokes in Costa Rica, including a cartoon showing a pack of Rottweilers defending Costa Rica's northern border.
Although there is a widespread impression among Costa Ricans that their safety net is being strained by Nicaraguans, some studies show that the latter are using services at rates well below their share of the population. Many Costa Ricans blame Nicaraguans for a surge in street crime, but prison statistics don't appear to bear that out either. From 1998 to 2003, Nicaraguans made up 5.8% of the jail population, according to the United Nations Development Program.
Immigrant advocates say Costa Rica's reforms aren't likely to stem the tide of job seekers.
Employers have come to rely on this cheap source of labor. And desperation knows no borders, says Gustavo Gatica, who works with Pastoral Social, an immigrants rights group affiliated with the Roman Catholic Church in San Jose.
"Even if they build a wall along the border with Nicaragua, like they have between the United States and Mexico, this won't stop immigration," Gatica says. "As long as there is hunger, as long as there is poverty, immigration won't be stopped."
Dickerson is a Times staff writer and Kimitch a special correspondent.