Boyd’s Bible Dictionary:
(blackness). The Sihor, or Shihor, of Egypt (1 Chron. 13:5; Isa. 23:3; Jer. 2:18), has ever been construed as “the Nile.” But when unqualified, some Arabian ravine or wady may be meant.
Concise Bible Dictionary:
Nile—Luxor
This refers to the river Nile. In Joshua 13:3 it is “Sihor which is before Egypt.” In Isaiah 23:3 the produce of the harvest of Egypt was brought to the sea by the river, and from thence was fetched by the Syrian merchants. In Jeremiah 2:18 Israel is warned against seeking the waters of the Nile; that is, trusting in Egypt instead of in God (compare Jer. 2:36). In 1 Chronicles 13:5 it is written SHIHOR, as the south-west boundary of Palestine. Some consider that Joshua 13:3 and 1 Chronicles 13:5 refer to the Wady el Arish, which was also called “the river of Egypt.”
Jackson’s Dictionary of Scripture Proper Names:
black: turbid