Why do rivers move a different speeds?

Well there are mamy reason...

1) how wide, big, and long the river is

2) Any hills or high points in the river from which the current can be increased

3) If their is something blocking the river ( like a beaver dam)

4) Even the wheather ( like if its windy the current will flow faster or vise versa if the wind is blowing against the current )

Current - The water flowing through the river