While not for the faint of heart, whitewater rafting is a great activity for those who are adventurous enough to give it a try. Whether you're a first-timer or a seasoned pro, it's hard to beat the thrill of cruising down a winding river, water splashing all around you anxiously anticipating the next set of rapids.  However, with so many rivers to choose from, it can often be a tough decision where to unleash your wild side. Are you a beginner looking for Class I and Class II rapids or are you a whitewater expert who is looking for their next big challenge?

From Pennsylvania and Oregon in the U.S. and Chile and Ecuador in South America, there are opportunities for whitewater rafting all over the world and if you know what you're looking for, the sky's the limit. Do you want a guided tour or do you and a group of experienced friends want to brave the waters yourself?  Here we look at some of the best whitewater rafting in the world- for beginners and experienced rafters alike.

Alsek and Tatshenshini Rivers, Alaska/Canada

Glaciers and icebergs are among the main attractions on these two rivers flowing through a breathtaking wilderness of mountains and tundra on the borders of Alaska and Canada. A trip through the upper Alsek is an incredible journey through one of the largest protected parks in the world. Beginning in Kluane National Park in Canada's Yukon, catch sight of spawning salmon or a grizzly bear as you wind through the Tatshenshini-Alsek Wilderness Provincial Park in British Columbia and ends in Alaska's renowned Glacier Bay National Park. A perfect excursion for the photography lover, wildlife is abundant with wolves, moose, deer and occasionally a wolverine. Float through the largest non-polar ice cap in the world through a spectacular 30+ miles of the lower Alsek River to Dry Bay with opportunities for a glacier walk along the banks. There are numerous tour companies that take trips along the Alsek and Tatshenshini, so you're sure to be able to find the perfect pace and level for you.

Middle Fork, Salmon River, Idaho

As one of the world's most popular whitewater rivers, the Middle Fork Salmon River has something for everyone. There are rapids up to Class IV and glorious alpine and forest scenery that flows through America's largest road-less wilderness area outside Alaska. Wildlife is abundant and can include the occasional mother bear and her cub swimming or the ever-popular moose and deer sighting. Middle Fork flows through the Frank Church River of No Return Wilderness, the largest forest in the lower 48 states and is the historical origin of white water rafting trips. Boasting 100 frequent rapids for over 100 miles, hot springs and reserved forest campsites, a trip down the Middle Fork Salmon typically starts at Boundary Creek boat launch, just below Dagger Falls. The first 22 miles to Pistol Creek Rapid are very fast as the rapids follow one another in quick succession. The alpine section offers class IV rapids that are continuous through Velvet Falls and Pistol. Velvet Falls, 5.5 miles from the put-in, is a short, steep drop into a river-wide reversal. The difficulty of the rapids may not be for beginners, but veteran rafters love the challenge and adrenaline-inducing speeds that the river has to offer.

Rio Upano, Ecuador

The Rio Upano or "River of the Sacred Waterfalls" offers a true sensory experience with nature, as rainforests engulf you with Toucans and iridescent butterflies. Starting in the remote town of Macas on the far western fringes of the Amazon Basin, you can embark on a journey where the pace varies from gentle rapids to tumultuous rides through narrow canyons. The Rio Upano treats you to Class II-IV whitewater rapids, mammoth waterfalls and glimpses of native Ecuadorian tribes. The highlight of the trip is the Namangosa Gorge, with Class IV rapids and a number of waterfalls plunging down the gorge's sides. This is a great river for beginners and experts alike, as it has challenging but manageable whitewater, in addition to good hiking trails and beautiful riverside camps when you want to take a break and enjoy the surroundings. Add in the area's amazing cultural history and contact with the Shuar Indians along the rivers banks and you've got a rafting adventure that's physically challenging and mentally and spiritually invigorating.

North Johnstone River, Australia

The North Johnstone is a steep, natural flow river that carves its way through a spectacular volcanic gorge. This stunning river in the tropical far north of Queensland offers Class IV and V whitewater rapids amidst the volcanic gorges and the ancient rain forests of Palmerston National Park. At night, rafters can view luminous fungi glowing on the rocks and fireflies dancing through the forest canopy. Best of all, you don't have to worry about what time of year to visit because the park and rapids are always in pristine condition. There is a limited frequency of departures, restricted group sizes and stringent National Park permits that ensure that the North Johnstone River and surrounding ancient rainforests are preserved, enabling rafters a rare glimpse of a very precious and untouched part of North Queensland's World Heritage Rainforests. Whether you're looking to challenge yourself with Class V rapids or simply want to float along and enjoy the breathtaking scenery, the North Johnstone River is one not to be missed for rafting enthusiasts.

Zambezi River, Zimbabwe/Zambia

Commercial rafting first began on the Zambezi River in 1981 and since then has grown in popularity to the point where a rafting trip on the Zambezi is now a regular feature in most tourists' itineraries. More than 50,000 people a year enjoy whitewater rafting on the river claimed as the best rafting trip in the world. Classified as a high volume, pool-drop river, there is little exposed rock either in the rapids or in the pools below, making it extremely challenging. The distance between rapids varies from 328 feet to 1.2 miles and the Batoka Gorge, where the Zambezi churns its way over 23 rapids, is approximately 400 feet deep at the put-in point and 750 feet at the take out point. The British Canoe Union has classified the river Grade 5, which means "extremely difficult, and has long and violent rapids, steep gradients, big drops and pressure areas." In fact, nearly half of the rapids you'll come across are Class V, which is the toughest you are allowed to raft. Due to the steepness of the gorge, wildlife is not abundant, but adventurous rafters should have enough adrenaline to make up for the lack of nature.