The Tarcoles River is one of Costa Rica’s biggest rivers and flows in the Pacific Ocean between Orotina and Jaco in the Province of Puntarenas. The river collects the rainfall of a wide and heavy populated area. Its watershed covers 50% of the population of Costa Rica and includes a big part of the Central Valley. It might come as no surprise that this makes the Tarcoles the most contaminated river of Costa Rica. Besides from sewage of the main cities it also suffered from the damage of an oil leak in 2000, when almost half a million litres of diesel flowed in the Tarcoles, because of an accident in Costa Rica’s state owned refinery. Despite the pollution the Tarcoles River hosts one of the world’s biggest populations of American Crocodiles, with an average of 25 per square kilometre. You can book a boat tour that will take on the Tarcoles River and enables you to observe these prehistoric reptiles that can measure up to 4 metres. Another more easy way to observe the crocodiles is from the bridge crossing the Tarcoles River when travelling on Route 34 from Orotina to Jaco. On both ends of the bridge you can park your car, walk on the balustrades towards the centre, from where you have a good spot to observe and photograph the humongous crocodiles in the water and sunbathing on the river banks. The Tarcoles River forms the northern border of the National Park of Carara, a more than 5,000 hectares protected area that contains in interesting transitional zone from the dry rainforest to the wet rainforest on the coastal plains. The meandering Tarcoles River forma a marsh delta with a unique ecosystem, and has many more interesting wildlife besides the crocodiles. The Carara National Park also has a rich pre-Colombian history. Archaeological finds traces of Indigenous inhabitants, occupying the area from 300 BC to 1,500 AD, making a living of agricultural activities.