goldminers. Illegal logging is not frequent, but the trees that are removed are scarce and essential to the ecosystem. Increased tourism has led to an increased presence of humans in the park, which may threaten the long-term survival of the park's larger mammals. To help combat the threat of over-exposure, many agencies and other groups (including Conservation International, The Nature Conservancy, WWF–U.S., rain-forest conservation groups in several countries, Catholic Relief Service, Organization of American States, and the Costa Rican, Danish, Dutch, Swedish and United States governments) have come together to provide aid to the conservation cause. Visiting Corcovado National Park is open to the public and can be visited on day trips and for overnight visits. As of February 1, 2014 all Corcovado visitors must be accompanied by certified professional guides. During the wet months (July to November) parts of the park may be closed. There are two tracks, one coastal and one inland, and four ranger stations in the park where one can stay overnight; three at the park entrances and one at the intersection of the two tracks. One track runs Northwest to Southeast along the coast to La Leona ecolodge, with the Estación Sirena roughly in the middle. The second track runs inland from Estacion Sirena to Estación Los Patos at the Eastern end of the park. On the coastal track there are several rivers that need to be forded. These rivers can all be very dangerous if forded at high tide or if one is inexperienced in this kind of an environment. Rio Sirena is commonly regarded as the most dangerous of crossings, primarily because it flows directly into the massive Laguna Corcovado in the isolated heart of the park. Bull sharks are present within the river and can sometimes be seen at the river mouth during high tide. American crocodiles are also present within the river. Spectacled caiman are present further up river and within Laguna Corcovado in larger numbers. The Rio Claro, which is approximately 40 minutes south of Rio Sirena, is said to be safer. Small American crocodiles and spectacled caiman are also present within the Rio Claro, albeit in smaller numbers than Rio Sirena. The Rio Madrigal, just north of the park entrance, is much smaller and may be home to spectacled caiman. References External links practical information for visitors extensive background information guide for visitors National parks of Costa Rica Protected