The Senegal is the only permanent river between southern Morocco and central Senegal. From its source in Guinea, it flows north and west , reaching the Atlantic Ocean at Saint Louis, Senegal. From its mouth, the river is navigable as far as Kayes, Mali, during the rainy season and Podor, Senegal, during the rest of the year. Heavy rains, beginning in April in Guinea and May and June in Senegal and Mali, bring annual floods. These floods cover the entire valley up to a width of , filling numerous lakes and sloughs (marigots) that empty back into the river during the dry season. A notable example of these is Lake R'Kiz. When the waters recede from the bottomlands, planting begins.