the estuary of the amazon is about wide. the width of the mouth of the river is usually measured from cabo do norte to punto patijoca. generally, the outlet of the para river is included. it is wide, and forms the estuary of the tocantins. the estuary also includes the island of marajó, which lies in the mouth of the amazon. this means that the amazon is wider at its mouth than the entire length of the thames river in england.