Scientists on a research voyage off Australia's east coast have been shocked to discover party balloons hundreds of kilometres from shore.

Dr Eric Woehler from Birdlife Tasmania has been aboard the CSIRO vessel, RV Investigator, observing sea birds and marine mammals.

On Sunday they made a startling discovery.

"We saw two groups of party balloons — one was a group of about 10 or so balloons still tied together and a smaller group of about three or four balloons tied together — and we were about 250 kilometres off the coast of New South Wales," he said.

Dr Woehler said balloons could have a devastating impact on the environment.

"The concern about these balloons in the ocean environment is that when they eventually deflate or when they're punctured for whatever reason, that fragments of the balloon will be seen as potential food by albatrosses, by turtles.

"There's a real risk that these balloons that have been released from the mainland that have drifted 250 kilometres over the ocean will end up in the stomach of seabirds or turtles."

The balloons were found floating 250 kilometres out to sea. ( Supplied: Eric Woehler )

Scientists recently drew a link between the amount of plastic a sea turtle consumes and its likelihood of death, with an estimated half of all sea turtles having plastic in their gut, according to CSIRO researchers.

Dr Woehler said seabirds were observed close to where the balloons were found.

He was surprised by the discovery and urged people to be environmentally responsible.

"It's mind-boggling that we've got balloons so far out in the ocean," he said.

"Ideally you should dispose of balloons appropriately when you're finished with them."

It's feared birds like shy albatross could confuse deflated balloons with food particles. ( ABC Open contributor ahsley_thomson2 )

Hobart mum Jessica Beavan bought balloons for her son Oscar's first birthday, but would consider not doing so again.

"I don't often buy balloons, but two weeks ago Oscar got his first balloon for his first birthday ... he loved it," she said.

"I'm always hearing about how much plastic there is in the ocean, it's pretty concerning.

"Most of us have let off a helium balloon like I did when I was a child without a second thought as to where it goes.

"I didn't think about it then but I wonder now where it's gone."