1 Nephi 8:13
13 And as I cast my eyes round about, that perhaps I might discover my family also, I beheld a river of water; and it ran along, and it was near the tree of which I was partaking the fruit.
The rivers in Lehi’s vision present an interesting problem. There seem to have been two very different rivers, and the differences between them are important to understand the meaning of the vision. The first river Lehi mentions is the one that ran near the tree of life. In all the scriptural references where both the tree and the river are mentioned together, the source of the river is either the place where the tree was found, or else under the throne of the Temple and near the tree. We later learn that the second river represents filthiness and the depths of hell (1 Nephi 12:15-18, 15:26-29). Nothing filthy can be where the tree of life is, so the filthy river must be different from the one that was near the tree, or else it becomes filthy as it moves away from the tree and encounters this corrupt world.