Marañón River
Fritz proposed that the Marañón River must be the source of the Amazon, noting on his 1707 map that the Marañón "has its source on the southern shore of a lake that is called Lauricocha, near Huánuco." Fritz reasoned that the Marañón River is the largest river branch one encounters when journeying upstream, and lies farther to the west than any other tributary of the Amazon. For most of the 18th–19th centuries and into the 20th century, the Marañón River was generally considered the source of the Amazon.