Watson was the center of a complaint received Feb. 4 by the Galveston Police Department.
After a preliminary investigation, police requested help from the Galveston County Sheriff's Office, who took a deeper dive into allegations against Watson.
Watson was arrested Tuesday by deputies.
He worked with the Investigative Services Bureau for more than 18 years.
Watson is now on paid administrative leave until the end of the investigation.
According to documents, the victim says Watson had been sexually abusing her since she was 13 years old. The victim is now 17 years old.
RELATED: Officer in training arrested after allegedly luring 12-year-old girl to Cypress hotel room