According to a report by TMZ, the girl was underwater for several minutes after an ATV she was riding flipped over.
Maddie is the niece of pop superstar
She was just 16 and engaged to Casey Aldridge, the father of her child. She's now married to Jamie Watson.
Maddie's grandfather, Jamie Spears, spoke to E! News Sunday, urging the public to keep his granddaughter in their prayers.
"All I can say is pray for our baby Maddie," he says.
Sources in the Kentwood, La., area say she was riding a Polaris ATV while on a hunting expedition. According to reports, Jamie Lynn was not with her daughter at the time of the accident.
Maddie was airlifted to a nearby hospital.
Late last year, Spears posted some images of Maddie on social media during family outings and shared her pride over her girl's accomplishments in school.
A photo posted by Jamie Lynn Spears (@jamielynnspears) on