Nearly 19% of the Nation's total area is covered under some form of environmental protection. The Department of Conservation and the Ministry for the Environment are the two leading government agencies responsible for this effort. According to the World Tourism Organization, tourism is going to be the biggest industry by the year 2001. As of 1990, the combined value of domestic and international tourism in New Zealand has been estimated to be $4,251 million. Even though tourism is one of the leading industries in New Zealand, much of it comes from domestic visitors. Of the 4 billion plus expendiute, about half comes from with the country. Australians are the common foreign visitors, leaving about $465 million behind after they leave. The United States, Japan, and the United Kingdom are respectively the next most common visitors. Visitors average about $2000 a trip each and spend almost a hundred dollars a day. Renting cars are organized bus tours are the most common way of traveling.