It happened in the 13000 block of Will Clayton Parkway at a private lot on Lake Houston.
According to the Houston Fire Department, the man -- identified by family members as David Andrew Flores -- was riding a jet ski when he reportedly fell off into the lake around 3pm Sunday.
Officials said a nine-year-old boy was riding with him. The child had a lifejacket and made it to shore, but Flores did not. He has been missing since.
HFD and assisting agencies had a boat in the water and crews on the ground conducting the search.
Watch the video for additional details from ABC13 reporter Andy Cerota, and stay with Eyewitness News and abc13.com for updates as they become available.