A couple of dolphins have been captured on camera frolicking in the Brisbane River near the CBD.

Videos and images have been shared on social media these past few days showing the dolphins as far upstream as the Victoria Bridge, connecting the CBD to South Brisbane.

So are they lost? Are they stuck?

Neither, says Queensland Museum's senior curator Dr Paul Oliver.

These dolphins were first spotted over the weekend. ( Instagram: brizzypix )

"They're probably bottlenose dolphins, they live along coastal areas and they're quite happy foraging in estuaries and along rivers, in particular rivers, they're a good source of food," Dr Oliver said.

"Our best guess is they're just feeding, that's what they do."

Dr Oliver said the river's mud-coloured waters would not stop the dolphins from seeking out fish to feast on.

"They send out high-frequency clicks from an organ in their head, and those clicks if there is something in the water they bounce back," he said.

"Basically the use sound to find things in the water. They can find things in areas where they can't see particularly well."

According to followers of ABC Brisbane's Facebook page, the dolphins have been hanging around the river since at least the weekend.

"We saw them Saturday afternoon while we were travelling on a CityCat," Emma Harding said.

Cheryl Thompson wrote, "[we] saw them Sunday near Gateway Bridge."

Dolphins in the Brisbane River is not totally unheard of, but it's not overly common either.

"I saw them about three years back, up at West End, couldn't believe my eyes," Tina Vagnini said.

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