NARANJO RIVER, Puntarenas –Barreling headfirst down white-waterrapids on a muscle-bound sled that floatswill usher in Costa Rica’s next wave ofextreme sports. The sport already latchedon in Europe, its pioneers began in the1980s and it is well-established in NewZealand and other countries – whereverthere is white water and thick skins.Now it is in Costa Rica for the firsttime – river sports fanatic Leo Vásquezhauled four boards from Italy where helearned to guide groups of boarders. It iseasy to learn, the equipment costs less thankayaks, and it is more thrilling than rafting,which is why when word gets out here andother river tour companies take notice, itshould be the next big thing within months.For beginners, the instruction beginsoutside the water and is continued in theriver. Vásquez starts out his lessons withsome variation on the four things toremember about riverboarding:1. Always hang on – or you’ll lose yourshield against the rocks.2. If you don’t keep your head up youmay lose your teeth – or you’ll just smackyourself a little.3. If you turn sideways in the currentyou’ll hit the rocks with your ribs insteadof the board.4. Take it easy – if you wear yourselfout trying to kick toward every wave onthe river you could be out of breath whenyou need to avoid some shallows or boulders.THE water is furious and the sport isjolting. It is challenging at first, but anyonecan learn it after a couple waves and dunks.The guides are always on hand in kayakspointing the boarders around the river’spitfalls and into the rollercoaster-likerapids. They become fast friends whentheir rolling lessons pay off the first time aboarder is flipped over a rock and careensdownstream upside down.“It’s taking rafting at a personal level,”Vásquez said. “It’s you with the river, rightthere.”The sport is not for everyone – unlike ariver raft that cushions the blows with twofeet of air and rubber, the board just hitsthings, shudders in the rider’s joints, andsometimes flips over (albeit rarely). It’s forpeople who are willing to take some hitsand enjoy a fast, gritty ride through therapids.“Going down the rapids the onlyengine is your legs,” Vásquez said. “Weteach you how to do it, of course, but goingdown the river it is only you.”IN Costa Rica, riverboarding beganwith Vásquez six months ago and is onlyoffered on about four kilometers (2.5miles) of this 12-kilometer (7.5 miles)stretch of the Naranjo River. Vásquez coownsH2O Adventures, the local branch ofRíos Tropicales in the Quepos-ManuelAntonio area on the central Pacific coast,the only company that offers the sport.Here, on a strip frequented by river raftsand kayaks taking advantage of the classesIII and IV rapids, riverboarders get a closeup,face-first introduction to one of thecountry’s wildest rivers.Riverboarders get tossed like gravel ina cement mixer at some of the frothwateredbends, and they spend some timewith their heads underwater, kicking theirfinned feet and squirming to right themselves.But if they remember to hang onthey can bang over the rocks in 007-stylewater sleds and float to calmer pools.Before catching their first currents,riverboarders have to strap on their armor.The suit is flippers, plastic shin and kneeguards wrapped tightly with Velcro straps,a life jacket and a helmet. Thin socks arerecommended to wear with the fins.THEY lay stomach-down on the boardand hang on to two metal grips, their legssprawling off the back where the shin andknee guards turn an otherwise bloodymauling by boulders in the river into forgettablebumps.Then the ride is wave-dunking, rock- skirting and rapid racing thrills broken by some leg-kicking between thewhite water and around the jams and shallows.The sport is also called water sledging and the boards are called hydrospeeds or riverboards. The boards can be made of plastic or foam – Vásquezplans on importing some made of foam to cut down on the bumps.BEFORE bringing the sport to Costa Rica, Vásquez trained in boardingsafety and guiding in Italy, where he lived and worked as a river guide.After undergoing four months of tests on Costa Rica’s rivers, withkayakers along for support and to lead the boarders through the river’sobstacles, Vásquez and company put the tour on the market only twomonths ago. The trip lasts about two hours with a stop for a snack.He and H2O’s other multilingual, tattooed, tough and funny internationalguide staff lead half-day to four-day rafting trips, teach beginningkayakers how to splash around in the rapids, take out groups of experiencedkayakers on the Naranjo and the Savegre rivers, and now lead riverboarderson the Naranjo, where the rapids are closer together and the excitementis more compact. The company also leads mellower sea kayaking tripsthrough the Damas Island estuary channels lined by mangroves teamingwith monkeys, and the Manuel Antonio coast, as well as another new sport:kayak surfing – when the waves are high.The company helps with vacation plans from half-day to 15-day itineraries,carting people around the country and providing transportation, lodgingand activities custom-suited to budgets and lifestyles.H2O is insured and is also registered with the Costa Rican TourismInstitute (ICT). The price for the new riverboarding adventure is $65 perperson.For info, call 777-4092, e-mail firstname.lastname@example.org, orsee H2O’s Web site at www.aventurash20.com.