The Park Service has not re-opened their longest and arguably most distinguished trail. The trail is reportedly to be closed permanently to the public. The only portion of the trail that is to remain open is the section from San Pedrillo to Llorona.
The trail connecting Sirena and San Pedrillo ranger stations is the most challenging of all the Corcovado National Park trails. It is 25 kilometers in length, crosses three major rivers, and is 75% along a beach. This trail is closed from April 15th through December 15th, and the Park Service is considering closing this trail permanently because of the following reasons:.
1) The separation of the three rivers requires careful planning to ensure hikers are not caught by high tide, when rivers are dangerous because of depth, currents, and because of the abundance of crocodiles and bull sharks that feed in the estuarine environment at high tide
2) There is no potable water for refills, meaning that hikers must endure the burden of at least four liters of water. For those that have water filtration or iodine tablets, there is a fresh water source 7 km from San Pedrillo, but for the 18 kilometers separating this stream from Sirena, all the rivers are brackish, so even water purification tablets are not help.
3) The eighteen kilometers separating Sirena Ranger Station from the Llorona River are all along a beach, and there is no protection from the sun. This means that the hike should only be taken at night.
4) The combination of circumstances makes this hike a dangerous one for unprepared hikers. It is a technical hike best undertaken with an experienced guide. However, it can easily be done by well-conditioned hikers that pay close attention to the guidance given in this section.
Sirena Ranger Station - Sirena River. The first twenty minutes of the hike is to the mouth of the Sirena River. This river drains Corcovado Lagoon and can be crossed at the river mouth only within three hours on one side or the other of low tide. To reach the crossing, simply follow the Sirena Trail that turns off of the landing strip about half way down its length to the right. It is a well marked trail. Upon reaching the Guanacaste Trail, turn left, walk another five minutes then turn right at the beach to reach the river mouth. Alternately, if it is possible to impose upon guests renting the Sirena River canoes to ferry your group across the river during the falling tide to give you more time to make the hike. To reach the Sirena canoe landing turn right on the Guanacaste Trail from the Sirena Trail rather than left and follow it five minutes to the canoe landing.
Sirena River -- Corcovado River. This 8.4 km stretch will take about 2.5-3 hours to hike and is all soft sand. It is the hardest part of the entire hike and is open beach with no protection from the sun. Cross the Corcovado River as close to its discharge to the ocean as possible as the river mouth is wide at this point. Even one meander or two upstream, a low-tide depth of two feet at the river mouth becomes a four foot depth in the deepest part of the channel. Do not search for a shallow portion upriver, as it only grows deeper.
Corcovado River -- Llorona River. This 8.1 km stretch will take 2 - 2.5 hours to hike and is all hard sand and easy walking. it is an open beach hike with no respite from the sun.
After crossing the Llorona River, there are no more tidally sensitive crossings. This is an excellent location to stop and rest until daybreak. The beach is very broad, and high tide does not reach the base of the forest. Where the trees start there are a number of spots that are convenient for resting with logs for sitting on and dry sand for sleeping. The Llorona Arch is located one hundred meters or so from the river at this point and is a landmark best appreciated in daylight.
About 700 meters beyond the Llorona River, the trail enters the forest and climbs for a forest traverse of about 3.5 kilometers. This portion of the trail passes through old growth primary rain forest and crosses a number of streams where fresh water can be secured, presuming that purification tablets or filtration equipment is used. The protozoan giardia lamblia is ubiquitous in the rivers and streams of Corcovado, and drinking stream water from any location, no matter how pristine the environment is sure to result in debilitating gastrointestinal stress. Giardiasis (beaver fever) is a persistent condition that can only be remedied through aggressive antibiotics and can be carried for years by unknowing victims, resulting in periodic bouts of diarrhea. Surface water should not be consumed without prior purification.
The trail rejoins the beach for another 1.5 kilometers of beach hike, and at the Pargo River, the trail turns into the forest once again for a gentle easy hike the remainder of the way into the San Pedrillo Ranger Station.
From San Pedrillo it is a 15 kilometer hike to Drake Bay. Guided tours are led in the San Pedrillo area on a daily basis by lodges and independent tour operators, and normally it is possible to get a boat ride to Agujitas (Drake) for a fee of $30 per person. These boats typically return from their tours at 13:30. For those planning to depart by this means, it is best to be in San Pedrillo early to secure space with the tour leaders or boat captains.