The footage captured earlier this week by Rich Horner showed him swimming in Manta Point, a famous diving site about 20km from the popular tourist island.
He told the BBC the sight was "horrifying".
Is it normal to see so much plastic in Bali's waters?
It's no secret that Bali has a problem with rubbish, but even Mr Horner, a Bali resident, said he had "never seen anything on this scale" before.
Similarly, a diving travel consultant in Bali told the BBC that it was "quite uncommon" to see such a large amount of rubbish.
"We had visitors go out to Manta Point just one day before Mr Horner did and they experienced beautiful waters," said Adriana Simeonova of the Aquamarine Diving Site.
Where is it all coming from?
Bali sits in the middle of the Indonesian Throughflow, a current that streams from the Pacific Ocean into the Indian Ocean through the straits of Indonesia.
This means that plastic waste could either be local or brought in from as far away as the Pacific Ocean.
"The plastic I saw mainly had Indonesian labelling but because of the current could be coming from anywhere in Indonesia, the Philippines, Malaysia [or] beyond," said Mr Horner.
This also means that the plastic could be swept away in a matter of a few hours or days - it all depends on the currents.
"The next day, divers who went to Manta Point report that they saw no plastic at all. Sadly [this means] the plastic is continuing its journey, off into the Indian Ocean," added Mr Horner.
What is the government doing about this?
Earlier last year, officials in Bali declared a "garbage emergency" across 3.7 miles (6km) of the island's beaches , deploying 700 cleaners and 35 trucks. On some days they collected up to 100 tons of rubbish.
But Ms Simeonova says the problem isn't just limited to Bali.
"There's a lot of cleaning initiatives around Bali and regular beach clean-ups, but the thing is that a lot of the rubbish is coming here from Java [Indonesia's main island]."
Indonesia's Minister of Maritime Affairs and Fisheries in a statement sent to the BBC, expressed sadness at the pile-up of rubbish in Manta Point, saying Indonesia "must make the ocean our front porch, not our backyard".
Indonesia is currently the second-largest plastic polluter in the world, coming just behind China.
It has said it aims to reduce marine plastic waste by 70% by 2025, but there is clearly a lot more work to be done.