Jamie Lynn Spears Struggled to Free Daughter from Safety Belt

Jamie Lynn Spears and her husband struggled to free 8-year-old Maddie from the submerged ATV for several precious minutes ... according to cops.

The Tangipahoa Parish Sheriff's dept says Maddie was driving the Polaris ATV shortly before 3 PM on Sunday when she swerved to avoid a drainage ditch. The Sheriff says that's when the vehicle flipped into the pond and immediately went under.

Jamie Lynn and Jamie Watson were about 100 yards away when Maddie and the ATV submerged. We're told they ran over to her within seconds, but struggled to free her from the ATV ... due to the safety belt and netting.

The Sheriff says Maddie was finally freed by paramedics when the ambulance arrived within just a couple minutes.

As we reported ... Maddie is currently in critical but stable condition in a New Orleans hospital.