Elephants occur across the entire north of Namibia with two main sub-populations in the north-east and the north-west. In 2004 the total population was estimated at over 16,000 animals and, allowing for underestimates on aerial surveys, the true number in 2007 is likely to be closer to 20,000. The north-western population is about 4,000 animals and includes the elephants in Etosha. This appears to be growing at about 3.3% per annum and expanding its range. Elephants are being seen as far south as the Ugab River and in all of the river catchments which flow westwards to the Atlantic Ocean in the north. As yet, the extreme north-western part of the potential range along the Kunene River has not been re-colonized although elephants were present in this area until 1990. The north-eastern population will probably reach 16,000 animals this year. The recent increases are well in excess of normal growth rates (which are less than 5% per annum) and must be attributed to the migration of the northern Botswana population (which consists of about 160,000 elephants) and the north-western Zimbabwe population of about 90,000 elephants.