Board Thread:General Discussion/@comment-6302057-20160307065615/@comment-6302057-20160328033519

Regardless of any speculation, as of 5x15 we can now canonically name four of the rivers: Only the lava river (likely to be Phlegethon) remains.
 * River of Lost Souls - green (named in 5x14)
 * Styx - blue (shown in 5x14)
 * Cocytus - grey (shown in 5x14)
 * Lethe  - yellow (shown in 5x15)