08/08/2012 05:01 pm ET Updated Aug 11, 2012

Christopher Marks Dead: Body Of Missing Missouri Boy Found In Meramec River

The body of 12-year-old boy who vanished on a family trip has been found in Missouri's Meramec River.

Christopher Marks of Affton, Mo., was reported missing on Sunday evening, when he disappeared during a picnic at the Pacific Palisades Conservation Area.

The search came to a tragic end when Marks' body was found in the river at about 5:30 pm on Tuesday, KDSK reports. Todd Combs, Marks' stepfather, discovered the body near a boat ramp access about six miles from where the 12-year-old had last been seen, according to Affton Patch.

Sister Katie Marks, 15, said her younger brother waded into the river at around 7:30 p.m., saying that he was going to go use a rope swing, and vanished moments later.

Search teams scoured the river and nearby area for two days. Marks' great aunt, Donna Sherman, had hoped she had found a positive sign yesterday when she located a tube of lip balm, believed to be her nephew's, on the ground.

See Photos From The Investigation (story continues below) :

Photos From Christopher Marks Search

Combs, Marks' stepfather, had been the only adult supervising the Sunday picnic, which included Marks and five other children ages 12-16. Katie Marks noted that her brother had consumed a small amount of beer that day, but that "it wasn't much."

At this point, St. Louis County Police Chief Tim Fitch told Eureka-Wildwood Patch, "it's hard to say if alcohol played a role in [Marks' death]."

Marks, who was enrolled to begin 7th grade in the fall, was described as "really, really funny"by members of his family. He was a Boy Scout who had undergone wilderness survival training and earned a swimming merit badge, leading family members to hope he had survived the waters of the Meramec.

It's unlikely that the river's current was strong enough to carry Marks 6 miles down the river, according to Chesterfield Patch. Investigators say that determining a time of death will help them figure out whether the body was transported by the current or some other means.

Officials currently believe that Marks' death was an accidental drowning, though the official cause of death has not yet been verified.

"We have no belief that foul play was involved at this time," Chief Fitch said.