larger waves, and if the rider is attached by a leash, he or she can be dragged for long distances underwater. Surfers should be careful to remain in smaller surf until they have acquired the advanced skills and experience necessary to handle bigger waves and more challenging conditions. However, even world-class surfers have drowned in extremely challenging conditions. Collisions Under the wrong set of conditions, anything that a surfer's body can come in contact with is a potential hazard, including sand bars, rocks, small ice, reefs, surfboards, and other surfers. Collisions with these objects can sometimes cause injuries such as cuts and scrapes and in rare instances, death. A large number of injuries, up to 66%, are caused by collision with a surfboard (nose or fins). Fins can cause deep lacerations and cuts, as well as bruising. While these injuries can be minor, they can open the skin to infection from the sea; groups like Surfers Against Sewage campaign for cleaner waters to reduce the risk of infections. Local bugs and diseases can be risk factors when surfing around the globe. Falling off a surfboard or colliding with others is commonly referred to as a wipeout. Marine life Sea life can sometimes cause injuries (Bethany Hamilton) and even fatalities. Animals such as sharks, stingrays, Weever fish, seals and jellyfish can sometimes present a danger. Warmer-water surfers often do the "stingray shuffle" as they walk out through the shallows, shuffling their feet in the sand to scare away stingrays that may be resting on the bottom. Rip currents Rip currents are water channels that flow away from the shore. Under the wrong circumstances these currents can endanger both experienced and inexperienced surfers. Since a rip current appears to be an area of flat water, tired or inexperienced swimmers or surfers may enter one and be carried out beyond the breaking waves. Although many rip currents are much smaller, the largest rip currents have a width of . The flow of water moving out towards the sea in a rip will be stronger than most swimmers, making swimming back to shore difficult, however, by paddling parallel to the shore, a surfer can easily exit a rip current. Alternatively, some surfers actually ride on a rip current because it is a fast and effortless way to get out beyond the zone of breaking waves. Seabed The seabed can pose a risk for surfers.