Around 9:30 a.m., a fisherman reported finding the bag in the water along a section of the river near West Brannan Island Road, according to Shaun Hampton with the sheriff's department.
While there is little information thus far regarding the remains, Hampton reports they were in different stages of decomposition.
As the Sacramento County Sheriff's Department investigated human remains, speculation about who those remains belong to hit hard in nearby Concord.
The bag floating on the river was found near the same area missing man David Kempker's vehicle was discovered. Kempker has been missing since mid-March.
FOX40 spoke with his mom, Janis Descalzo, Monday on the phone regarding Sunday's discovery.
"We thought the worst. It seemed likely given the area where David's truck was found and where these remains were found," Descalzo said. "It's relatively close. It's not directly in the same area."
While the coroner in Sacramento County has yet to identify the remains, as of Monday afternoon Descalzo said she was informed by a detective with the Concord Police that his initial inclination was that the body found was not that of Kempker.
"He did indicate that he did not believe at this point that the remains found in Isleton belong to David," she told FOX40.
But without any official confirmation one way or another, Descalzo is stuck in limbo.
"If it ended up to be him at least it would be closer," Descalzo said. "It's not the ending I want but at least I'd know."