Their quills actually help them float! The quills have a spongelike filling inside. They can use their quills to float on rivers and streams to eat all the water plants. Porcupines have 30,000 of these quills. They use them for defense, though, unlike what you may have seen in the cartoons, they can't throw them at their enemies.
There are also some porcupines that have prehensile tails (like monkeys) and they can climb trees! Tree porcupines can be found in Mexico and South America. There are actually a lot of different species of porcupines, and they can be found in the Americas, Europe, Asia, and Africa.
Everything you ever wanted to know about porcupines.