Appears to be located at the four mile bridge.

http://www.civilwaralbum.com/vicksburg/camp_fisk1.htm

http://civilwartalk.com/threads/camp-fisk-prisoner-of-war-exchange-camp-at-vicksburg.116678/

http://civilwartalk.com/threads/prisoner-exchange-talks.23721/

http://www.loc.gov/pictures/item/90709414/