Chief Deputy Dale Rogers says they decided to charge David Persons, 31, of Boise, after they determined that he was driving under the influence and without privileges at the time of the crash.
Rogers says Persons' BAC tested at .087. The legal limit in Idaho is .08.
Persons was arrested in Boise on Tuesday afternoon and booked into the Ada County Jail.
The Boise County Sheriff's Office says Pearl Sittner, 4, of Boise, was in the SUV with four other family members last August when it went off the road and slid 90 feet down an embankment before stopping.
The girl's parents were able to get two other children out of the SUV, but were unable to reach Pearl before the SUV broke loose and slid another 60 feet down the embankment into the water.
Officials estimate the SUV sank 40 feet into the water. Divers arrived at the scene and found Pearl still inside the SUV. They brought her to the shore and started CPR, but it was too late.