At the edge of the Pacific, where the Tarcoles River meets the ocean and route 34 breaks from the mountains, there is an infamous highway bridge. People come from miles around to see the crocodiles beneath.
Stumbling from our "Tourismo bus" our guide shouts, "Heeey you bad boys, you want cerveza? Imperial is good, yes? Here, eets for you!"
He tosses his half empty beer can over the guardrail. On a sandbank 7m below clunk! Fizz! Nothing! Like sodden grey logs they lie there with their mouths wide open. The sandpipers skitter between picking fetid shreds of decaying flesh from their jaws.
Litter is an obscenity, especially as Costa Rica's economy depends upon a pristine environment, so I am tempted to retrieve the can. But better judgment prevails.
The appearance of relaxed indifference is purposeful. Wound tight as a steel spring, an apparently dozing crocodile can explode into a deadly blur of snapping jaws. A large dog bites at 100 PSI (pounds per square inch); a crocodile delivers a bone splintering chomp at 3000 PSI.
Thick reeds line the shore and somewhere within, Tyson, a local celebrity, lays waiting. He is said to be at least 6m in length and on a number of occasions has invaded the nearby town on dog-snatching forays.
For those who come to experience the wildlife, Costa Rica's rivers provide the most immediate transition from urban bustle to rustic paradise. Many seek challenging wilderness adventures while others are just happy to ride a river boat through the local mangrove swamp.
The crocodiles are an endless source of horrified fascination. The muddy estuaries and placid channels are also a bird-watchers paradise. And there is some amazing whitewater rafting. There's great whitewater rafting in New Zealand, of course, but it doesn't have the added frisson provided by all those crocs, so before heading down the Pacuare River we pay close attention as Mauricio, our pilot, clips my wife Maggie's life jacket together.
"This is very important; it is the only thing that stops us drowning if we fall out. In the river we keep our feet downstream and we stay happy."
With naivety and innocence we push our flimsy little boat out into the current.
At the upper end of the gorge, with a watery slurp, our boat is sucked into the rocky gullet. It is pure whitewater heaven. We are irrevocably committed to 31km of jungle-shrouded canyon.
Jelly-green water is pounded into foam amongst bus-sized boulders. In the jaws of "Cimarron", an especially ferocious rapid, Maggie is tossed from her floppy rubber perch at the back of the boat. I watch in horror as her orange helmet disappears beneath the froth. She surfaces briefly and Jose Pavlo, in the accompanying safety kayak, noses toward her. "Look at me, Look at me", he screams, "Grab the boat!"
If it were not for his Herculean efforts she would never have escaped the river's grip. As she lies choking in the bottom of our raft, Mauricio, a master of understatement leans over her, "You are back in the boat now Maggie, try and stay with us".
Meanwhile, along the river bank naked Indian children splash in eddies. A gent in rubber boots and a loin cloth watches the strange visitors from his banana leaf shelter.
Later, as we raft the Sarapiqui, we drift through primeval, steamy jungle. Thirty metres above in the branches of an ancient tree the pendula nests of the Montezuma oriel sway in the breeze. At water level the sweat-soaked river explorer could only wish for such ventilation.
Three locals float by on an undersized inner tube. They fish for dinner in rather precarious circumstance. A 4m crocodile studiously ignores our boat's passing wake. "Don't worry, they eat only dogs", our guide explained. I wonder if the crocodiles know that.
At the inner elbow of the Nicoya Peninsula a canopied river-boat ferries tourists up the Tempisque. The Palo Verde National Park lies at the water's edge.
"This ees the most important park in Central America", our guide Jason explains, "When there is snow in Canada, all the birds come here".
The heat is suffocating and a column of long-nosed bats shelter in the coolness under a sagging tree trunk. Apparently they cluster in linear groupings for camouflage. Several bats line up nose to tail appearing as though they were a snake. When one moves they all move a sinuous reshuffling in the shadows.
From above there is a harsh roaring sound like a pride of angry lions in the trees. We fearfully scan the branches and the only thing we see is a diminutive black figure the howler monkey. In our confusion we discount his appearance and look for something more ferocious. Unsatisfied by our presence he soon gives himself away with another terrifying bellow.
The howler is big on noise but tiny in stature. Jason, our guide on the Tempisque River says, "They sleeps 15 hours a day. They ees very lazy. Here in Costa Rica we have a name for these. You know what we call them? Government workers! Like your country, si!"
RIVER EXCURSIONS IN COSTA RICA
Sarapiqui River Tour: On an arranged trip to the Poas Volcano the visitor will tour the lower crocodile infested waters of the Sarapiqui on a canopied river boat.
Rafting on the Sarapiqui: The Sarapiqui River is placid (Class 1 and 2) and beginners will feel comfortable on this tour. It is possible to see monkeys, toucans and otters along the banks.
Rafting on the Reventazon: Safe and enjoyable white water (Class 3) and plenty of wildlife in the surrounding forest. Tour companies offer more extreme trips for experienced rafters.
Rafting on the Pacuare: For its fantastic scenery, the Pacuare is considered to be amongst the best whitewater experiences in the world.
River Boat Tour on the Tempisque (Palo Verde): This is one of the premier bird watching sites in the Americas.
Crocodile Safari: This is a great opportunity to see some of the huge monsters that skulk around the mouth of the Rio Tarcoles, up close and personal.
Further information: There are numerous whitewater rafting companies in Costa Rica. Useful websites include exploradoresoutdoors.com, arenal.net, toenjoynature.com, junglecrocodilesafari.com and rainforesttours.com.