Web Author's Notes:
This wider view map shows the complex river structures surrounding Arkansas Post. Note the "cut off" between the White River, where McClernand took his fleet on approach to Arkansas Post, and the Arkansas River which lead the fleet to the fort.

Blue star - mouth of Arkansas River on the Mississippi River; the Union fleet bypassed this logical route to Arkansas Post to mislead the Confederates.
Green star - mouth of White River on the Mississippi River; the Union fleet entered the White River here in its approach to Arkansas Post
Yellow star - the "cut off", a navigable bayou connecting the White River to the Arkansas River and through which McClernand's fleet passed
Red star - the site of Arkansas Post or Fort Hindman, held by Confederates but captured by McClernand's forces on January 11, 1863

The following map from Zealby.com