Dead bodies do not immediately float. It can take between 12 hours to 12 days BEFORE a body will float."The body was discovered by a volunteer who was using a kayak on the river about 300 feet from where the boy was initially reported missing, the police department's Facebook post stated."
How does it take over a week to find him when he is 300 feet from where he came up missing?
When a person drowns, the body is filled with water which causes one to sink. As the bacteria eat the body away they produce gases inside the corpse. That gas not having a natural way to escape (burp, farts) will continue to build up inside the corpse, bloating it and causing enough of a buoyancy to make the corpse float.
If enough time passes with no way for the gases to escape the corpse will "explode" as the gas forces it's way out of the rotten weaken flesh that it was enclosed in.
Sadly this family will not get to see the body nor have an open casket for a funeral. The body will be in such a horrible state that no parents should have to see that as the last image of their child.