With the help of a police escort, about 100 protesters closed down two lanes of traffic on San José's Avenida Segunda on Monday afternoon to denounce a bill that would downgrade Las Baulas National Park in the north-western province of Guanacaste to the less restrictive status of a wildlife refuge.

The new status would permit development inside the limits of the park, which is dedicated to the preservation of the critically endangered baulas, or leatherback turtles.

Locals from Guanacaste, many clad in brightly colored traditional Costa Rican dress, joined members of environmental groups – some donning full turtle suits – in a march toward the Legislative Assembly, where the group demonstrated their concerns over the bill.

Raquel Villafuerte, a Guanacaste native who participated in Monday's march, said she is afraid that the change would deliver a serious blow to one of the area's main sources of income – tourism.

“It's absolutely necessary to protect the leatherbacks because a lot of our local economy depends on them,” said the 17-year-old, who wore a bright blue, green and pink dress. “Construction will destroy the park. No parks, no tourism. No tourism no money. The Legislative Assembly shouldn't approve this bill.”

The bill is in discussion in the various committees of the Legislative Assembly. In addition to allowing building within the area's limits, the bill also aims to remap the boundaries of the park.

Politicians have said the change is necessary to avoid having to hand over millions of dollars to landowners to expropriate the private property that already exists inside the park.

Some environmentalists fear that redrawing the park's limits and allowing construction would harm the habitat of the leatherbacks.

Maureen Ballestero, the president of the Environment Commission and a National Liberation Party legislator, has said she is not in favor of expropriating private lands in the park, but concedes that changing the status may not be the best option.

David García, 38, a passerby, said Monday's rally was the first he'd heard of the bill.

“It doesn't seem right, really,” said the San José resident, as he read a purple protest flyer. “It seems to me that we should support our national parks and I don't think this project is justified.”