"Do not touch the water while rescuing Terry" is an optional objective in the mission River Rescue
Follow the steps in the screenshots below to to rescue Terry without touching the water. You must be quick, so it is recommended you pause the game and thoroughly study the steps below before attempting:
Contents
Steps 1 to 4
Steps 5 to 6
Step 7
Steps 8 to 9
Step 10
Go UNDER the first tree log
Steps 11 to 12
Steps 13 to 14
Between the next two steps, use tree branch to help propel you to the next log
Steps 15 to 16
Step 17
Steps 18 to 20
Steps 21 to 22
NOTE: After the last step (Step #22) the cinematic will show Connor diving into the water to save Terry. This is OK.