live in the lowlands near the western coast of the island. The island is highly urbanized, with nearly 9 million people living in the Taipei–Keelung–Taoyuan metropolitan area at the northern end, and over 2 million each in the urban areas of Kaohsiung and Taichung. Taiwanese indigenous peoples comprise approximately 2% of the population, and now mostly live in the mountainous eastern part of the island. Most scholars believe their ancestors arrived in Taiwan by sea between 4000 and 3000 BC, most likely from southeastern China. Han Chinese make up over 95% of the population. Immigrants from southern Fujian began to farm the area around modern Tainan and Kaohsiung from the 17th century, later spreading across the western and northern plains and absorbing the indigenous population of those areas. Hakka people from eastern Guangdong arrived later and settled the foothills further inland, but the rugged uplands of the eastern half of the island remained the exclusive preserve of the indigenous peoples until the early 20th century. A further 1.2 million people from throughout China entered Taiwan at the end of the Chinese Civil War in 1949. Environmental issues Some areas in Taiwan with high population density and many factories are affected by heavy pollution. The most notable areas are the southern suburbs of Taipei and the western stretch from Tainan to Lin Yuan, south of Kaohsiung. By the late 20th century, Taipei suffered from extensive vehicle and factory air pollution, but after the government required mandatory use of unleaded petrol and established the Environmental Protection Administration in 1987 to regulate air quality, the air quality of Taiwan has improved dramatically. Motor scooters, especially older or cheaper two-stroke versions, which are ubiquitous in Taiwan, contribute disproportionately to urban air pollution. The Taichung Power Plant also contributes significantly to air pollution, producing more than the country of Switzerland. Other environmental issues include water pollution from industrial emissions and raw sewage, contamination of drinking water supplies, trade in endangered species, and low-level radioactive waste disposal. Though regulation of sulfate aerosol emissions from petroleum combustion is becoming stringent, acid rain remains a threat to the health of residents and forests. Atmospheric scientists in Taiwan estimate that more than half of the pollutants causing Taiwan's acid rain are carried from China by monsoon winds. Taiwan historically had a serious problem with the illegal dumping of household and industrial waste which became so severe that Taiwan was