John Gill Commentary Joshua 16:8

"From Tappuah the border went along westward to the brook of Kanah; and the goings out thereof were at the sea. This is the inheritance of the tribe of the children of Ephraim according to their families;" — Joshua 16:8 (ASV)

The border went out from Tappuah westward
Which was different from the Tappuah in the tribe of Judah, (Joshua 15:34) ; this was in the tribe of Ephraim on the border of Manasseh, (Joshua 17:8) ;

unto the river Kanah ;
supposed by some to be the brook Cherith, by which Elijah hid himself, (1 Kings 17:3 1 Kings 17:5) ; though objected to by others; it seems to have had its name from the reeds which grew in it, or on the banks of it:

and the goings out thereof were at the sea ;
if the river Kanah was the brook Cherith, this must be the dead or salt sea: but that is never called "the sea", rather the Mediterranean sea is meant, and consequently Kanah could not be Cherith, which was at too great a distance from this sea:

this [is] the inheritance of the tribe of the children of Ephraim by
their families ;
that is, this is the description of the border of it; for the cities within are not mentioned, and the descriptions in general are very obscure.