The Tigre reference article from the English Wikipedia on 24-Apr-2004
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Tigre

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The Tigre is a tributary to the Amazon River west of the Nanay, and is navigable for 125 miles from its confluence with the Amazon. Like the Nanay, it flows entirely on the plains. Its mouth is 42 miles west of the junction of the Ucayali with the Amazon. Continuing west from the Tigre we have the Parinari, Chambira, and Nucuray, all short lowland streams, resembling the Nanay in character.