This is what I found but lakes can also have their own rules.

A Federal Regulation went into effect May 1, 1995, which requires operators of all boats to have at least one wearable life jacket or personal flotation device, for each person aboard. Under the new regulation a throwable PFD (Type IV) will no longer qualify as a life jacket on boats less than 16 feet.



Laws for Required Wearing of PFDs :
In addition to the federal PFD carriage requirements, Mississippi has the following requirements for wearing a PFD:

Children 12 years of age and younger are required to wear a Type I, II, or III U.S. Coast Guard approved PFD whenever underway in a vessel under 26 feet in length. Children’s PFDs must be securely fastened and be size appropriate for the wearer.
Every person on board a personal watercraft (PWC) or being towed behind a PWC must wear a Coast Guard approved PFD. Inflatable PFDs are not intended for use while participating in tow sports or other high impact sports.
Children 12 and under must wear a PFD underway in boats less than 26 feet!