When the congo river reaches kinshasa,
it flows into a large lake
it flows slowly into the atlantic
its course is blocked by cataracts
it becomes an irrigation canal

If my memory serves me well, the answer should be: When the Congo River reaches Kinshasa, it flows slowly into the Atlantic. Congo River is the second largest lake in the world. It takes a long way to reach the Atlantic: In the middle it flows towards Matadi and divides into several arms and finally it freely flows into the Atlantic.