Namibia is a large country in Southern Africa that borders the South Atlantic Ocean, between Angola to the north and South Africa to the south. With a surface area of 824,290 square kilometers, it is similar in size to Mozambique and about half the size of the U.S. state of Alaska. Namibia has a small population of approximately 2.1 million people. It is also one of the least densely populated countries in Sub-Saharan Africa, with an average density of approximately 2.5 people per square kilometer, compared to 34 people per square kilometer for the region as a whole. Namibia was the last colonized country in Sub-Saharan Africa to become independent. After nearly 70 years of South African rule, Namibia gained its independence on March 21, 1990. Until 1990, Namibia's official languages were German, Afrikaans, and English. Following independence, English became the official language, although it is the first language of only a very small percentage of Namibians. Oshiwambo dialects are the mother tongue of approximately half of the population. Namibia, a lower-middle-income country, has one of the highest levels of per capita income in Sub-Saharan Africa. Namibia is one of very few countries in Sub-Saharan Africa that maintains a social safety net for the elderly, the disabled, orphans and vulnerable children, and war veterans. It also has a social security act that provides for maternity leave, sick leave, and medical benefits. Namibia has one of the most productive fishing grounds in the world. The fishing industry is an important source of foreign exchange and a significant employer. The tourism industry in Namibia is similar in size to that in Botswana and is the country's third-largest foreign exchange earner. Namibia is one of the largest producers of gem quality diamonds in the world. It is estimated that 98 percent of its mined diamonds are gem quality. In 2006, almost half of total production was recovered from offshore sources. Namibia is the driest country in Sub-Saharan Africa, with deserts occupying much of the country. It has no perennial rivers or any other permanent water bodies. Due to the low and erratic rainfall and scarce ground and surface water, less than five percent of the country is arable, including through irrigation. Namibia was the first country in the world to incorporate environmental protection into its constitution. Nearly six percent of its land is nationally protected, including large portions of coastal areas within the Namib Desert.