A pod of dolphins was trapped in fresh water.

Young Oliver Avard has had an emotional experience he's not likely to ever forget.

Three times a day, every day for an entire week, the 11-year-old, who was spending a week at his grandparents' property near Brushy Cutting on the NSW mid north coast stood on the banks of the Manning River keeping an eye on a pod of bottlenose dolphins that had become stranded in the river.

It ended up being a tragic ordeal for the entire family, as the dolphins started dying before help arrived.

"This was horrific. It was like someone died. We cried all of the first week. We became very invested," Oliver's mum, Jennah said.

Although it is not known for certain how the dolphins came to be so far upriver, the theory is that they came in on a super high tide chasing bait fish, but were not able to go back down river once the tide had abated, due to a shallow rocky section of the river near The Bight in Wingham.

Originally two pods were sighted at the Brush Cutting location, however one pod managed to make it out while the other pod of five dolphins could not.

The two pods were first spotted by a neighbour on September 4, who saw the second pod quickly move out. A kayaker reported a dead dolphin in the river on September 9.

Oliver and his family watched the situation overnight, and in the morning, not knowing who to call to get help, called Irukandji Shark and Ray Encounters in Port Stephens.

"And then it kind of just for us spiralled from there, that we just kept trying to advocate them," Oliver's mum, Jennah said.

National Parks and Wildlife Service (NPWS) and ORRCA became involved, monitoring the dolphins via a drone.

"Human intervention, including capture and release, poses a significant risk to dolphins and a positive outcome is not always guaranteed," NPWS said in a media statement.

NPWS hoped the dolphins would move back downstream of their own accord, however, tidal conditions did not allow that to happen.

The remaining dolphins quickly showed evidence of being sick, and tests on water salinity showed they were in fresh water.

The water had originally been assumed to be brackish.

Over the following week, all but one of the dolphins died, and it was evident the last remaining one was very unwell.

NPWS and ORRCA decided that, with the help of SeaWorld, a rescue of the remaining dolphin would be attempted.

On Sunday, September 17, seven days after the first dead dolphin was found, the team was able to rescue the surviving dolphin.

Sadly, as it was being transported to SeaWorld, the dolphin died.

A necropsy on the dolphin's body showed that the animal's organs had shut down; the rescue was too late.

In hopes that this will never happen again, Jennah has set up a community Facebook page, Manning River Watch, with the aim of keeping watch on dolphins in the river, and so people will know who to contact immediately should they suspect something is not right.

Jennah has been told of a similar stranding of dolphins in the river some 15 years ago.

The Manning River Times is seeking comment from NPWS, ORRCA and SeaWorld.

IN OTHER NEWS: