Where is the longest river in the world?

The title of longest river is debated, but the Nile in northeastern Africa is the traditional answer, measured at roughly 6,650 kilometres as it flows northward through countries including Uganda, Sudan, and Egypt before emptying into the Mediterranean Sea. Some researchers argue that the Amazon in South America, at around 6,400 to 7,000 kilometres depending on where its source and mouth are defined, may actually be longer. The uncertainty arises because rivers have many tributaries and shifting channels, and defining a precise source and endpoint is difficult. Regardless of which is longest, the Amazon is unquestionably the largest river by water volume, discharging more water than the next several largest rivers combined. Both rivers have been vital to civilisations, ecosystems, and economies for thousands of years.