Ice fishing is the practice of catching fish with lines and fish hooks or spears through an opening in the ice on a frozen body of water. Ice fishers may fish in the open or in heated enclosures, some with bunks and amenities. Shelters Longer fishing expeditions can be mounted with simple structures. Larger, heated structures can make multiple day fishing trips possible. A structure with various local names, but often called an ice shanty, ice shack, fish house, shack, icehouse, bobhouse, or ice hut, is sometimes used. These are dragged or towed onto the lake using a vehicle such as a snowmobile, ATV or truck. The two most commonly used types are portable and permanent. The portable houses are often made of a heavy material that is usually watertight. The two most common types of portable houses are those with a shelter that flips behind the user when not needed, or pop up shelters with a door as the only way out. The permanent shelters are made of wood or metal and usually have wheels for easy transport. They can be as basic as a bunk heater and holes or have satellite television, bathrooms, stoves, full-size beds and may appear to be more like a mobile home than a fishing house. In North America, ice fishing is often a social activity. Some resorts have fish houses that are rented out by the day; often, shuttle service by Snow Track or other vehicles modified to drive on ice is provided. In North America, portable houses appear to create a city at locations where fishing is done. Fishing equipment Ice fishing gear is highly specialized. An ice saw, ice auger or chisel is used to cut a circular or rectangular hole in the ice. The size of the hole depends on the type of fish sought, generally suggested is 8 inches (20 cm). Power augers are sometimes used. If these tools are not available, an axe may be used to chop the hole. A skimmer, a large metal spoon with holes in it, is used to remove new ice as it forms and to clear slush left from making the hole. During colder periods most ice anglers choose to carry a heater of some type. The heater is not only for warmth but also for keeping an angler's fishing hole from freezing. When temperatures fall to -20 °F (-29 °C) or