Lake Malawi, also known as Lake Nyasa in Tanzania and Lago Niassa in Mozambique, is an African Great Lake and the southernmost lake in the East African Rift system, located between Malawi, Mozambique and Tanzania. Lake Malawi is a meromictic lake, meaning that its water layers do not mix. The permanent stratification of Lake Malawi's water and the oxic-anoxic boundary (relating to oxygen in the water) are maintained by moderately small chemical and thermal gradients.