The other main tributaries of the River Nigeria are the Sokoto, Kaduna and Anambra Rivers. From Lokoja, the Niger flows southwards to the Delta, splitting into numerous interlacing channels to empty itself into the Gulf of Guinea. A Lake, with an area of 1,236 square kilometers, was created on the River Niger by the construction of the Kainji hydro-electric dam, about 112 kilometers north of Jebba. The dam, which is also being used to control the flow of the Niger flood waters, has now made the river navigable throughout the year from Escravos to Niamey in the Niger Republic, a distance of more than 1,600 kilometers. The temperature is always warm.
Precipitation diminishes rapidly from the coast inland.
There is usually heavy rainfall in the south west while a secondary rainy season normally occurs in the second half of September and October. However, in the south-east, there is only a single rainy season from May to October. This period further shortens from June to September in the far north. Over 250 different ethnic nationalities live in Nigeria. Other groups are quite small.