Fatal freak accident unfolded hours after female Marine veteran, 63, posed for this photo with her beloved dog

A retired marine and her dog have drowned in a freak rafting accident on a fast-flowing river they float down every year.

Mary Marshall, 63, was rafting with a dozen friends and her German Shepherd named Suki on Kings River in Reedley, California, on Saturday.

The former sergeant posed for a happy snap with Suki on the raft before the group set off, smiling ear-to-ear excited about the annual trip.

Tragedy struck after the group's lunch stop when the current veered her raft into a tree sticking out of the river, and it got stuck.

Mary Marshall, 63, posed for a happy snap with her German Shepherd named Suki on the raft before the group set off, smiling ear-to-ear excited about the annual trip

Marshall was rafting with a dozen friends on Kings River in Reedley, California

Marshall, from Menifee, California, had tied her raft to another raft and secured Suki's leash to a harness she was wearing - but not a life jacket.

Suki jumped off the raft when it was stuck against the tree, but this overbalanced the raft and flipped it, sending Marshall into the water - and pulling the dog with her.

'Both then got stuck in a strainer, a turbulent flow of water against an object that is difficult to escape,' the Fresno County Sheriff's Office explained.

'The leash became wrapped around a tree branch underwater, causing Marshall and her dog to remain submerged.'

Marshall's panicked friends called for help about 3.30pm and deputies searched for two hours before finding their bodies about 6.30pm.

Suki was still attached to her beloved owner and police had to cut the leash to bring them both to the surface.

Tragedy struck after the group's lunch stop when the current veered off course

Marshall was a US Marine Corps sergeant, posing here with a comrade during her active service

'There's a lot of trees in the waters, they're called an undercut where you can get stuck in there and we believe that's what happened,' deputy Chris Tellus said.

'The water is going to push you wherever the water wants to push you, it just pushed her down.'

Marshall's friend Kevin Horn, who was also on the river that day, said the group made the trip every year for almost two decades and she often took charge.

'Mary was always the heart and soul of these trips, taking charge like the Marine she was,' he said.

'That morning, her excitement was contagious as she kept saying to everyone, "We're going to have so much fun".'

'Mary's love for these trips was matched only by the love she had for all of us.

'Mary was a Marine, a fierce protector, and a loving friend. Her loss is immeasurable, but we will carry her spirit with us always.'

Friends said the group made the trip every year for almost two decades and she often took charge

Deputies searched for two hours before finding their bodies about 6.30pm

Other friends paid tribute to Marshall and shared their memories of her on the river and on dry land.

'I am so sad, I love Mary and every time I'll see her she was a joy to be with even though we always fight for left over food to take home,' one wrote.

Another added: 'She was surrounded by people she loved doing what she loved. 

'I recall a river trip where she injured her hand and used duct tape to wrap it, earning her the nickname "Mary MacGyver" that weekend.'

Police warned anyone floating on the river to stick to the center of the river to avoid trees, and never to tie rafts together.

'This creates a dangerous situation because if one floater experiences a problem, all others will as well because they do not have independent control of their rafts,' they said.

They also suggested fitting life jackets to dogs if they were joining the flotilla.