Which body of water is the nile river's primary reservoir?

Lake Victoria is the Nile River's primary reservoir

Explanation:

The Nile River starts to flow as river from the Lake Victoria present in the today's Tanzania, Uganda and Kenya region. It passes via Egypt and ends or mixes up in the Mediterranean Sea.

It is the world's longest river due to the fact that it flows for over 6600 kilometres (4100 miles). River Nile consists three tributaries as the Blue Nile, Atbara, and White Nile.

The Blue Nile begins at Lake Tana in Ethiopia and flows into Sudan from the southeast. The two rivers meet just north of the Sudanese capital of Khartoum. The northern section of the river flows north almost entirely through the Sudanese desert to Egypt, then ends in a large delta and flows into the Mediterranean Sea.