In waters across the Pacific, an untold amount of black, toxic oil is contained within the corroding wrecks of World War II ships. And it’s leaking into the ocean.
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Inside the murky hull of a Japanese transport ship, 25 metres below the water's surface, a diver reaches out towards a black glob on the roof.
As he touches it, little dark bubbles of oil jump about in the water.
He rubs his fingers together. They are covered in sticky sludge.
The diver is Neil Yates. He has owned a scuba company in Solomon Islands for 17 years and is showing me some of the country's most popular dive sites.
"What we saw will hopefully come out as little bubbles, not a big oil slick — it would stain about half the beach," he says.
While the fish and coral in Solomon Islands are beautiful, we're not here for that.
We're looking for oil.
Sixty metres below the surface, inside the wreck of an oil tanker, Neil enters one of the fuel bunkers.
It's empty – the oil that was inside up until just a few years ago has washed away.
But it's just one of several bunkers on this ship.
"We can't see into all of the holds on this ship … [but] being an oil tanker, yes there is definitely going to be oil in it," he says.
We're in Iron Bottom Sound — a stretch of water in Solomon Islands off the coast of the capital, Honiara.
It's a mecca for serious scuba divers.
Lying on the sea floor below us are dozens of ships from four countries — the United States, Japan, New Zealand and Australia — sunk during ferocious battles in World War II as the US and its allies tried to take Solomon Islands back from Japanese forces.
The battle of Guadalcanal — the largest island in thearchipelago and now home to the capital city, Honiara — was a turning point in World War II.
It was the first time US troops had invaded Japanese-held territory and sparked a ferocious series of battles on land, in the air, and at sea.
By the time the US and allies pushed the Japanese off the island and the battle ended, around 30,000 men had been killed and more than 1,000 planes and ships were destroyed.
The wrecks have been rusting away on the sea floor for more than 80 years.
Many of the divers who come here know they are seeing a piece of history that won't last forever.
"We're in an exponential stage of erosion, and I think it's only going to get worse now, unfortunately," says Aron Arngrimsson, an underwater cinematographer who is travelling across the Pacific recording extremely high-resolution images of the World War II wrecks.
When these now-corroding ships sank, they each had an unknown amount of fuel on board.
Some of that oil has leaked out over the years, but there are fears a lot more remains.
"There's still a lot of oil on things around here," says Neil.
"The total quantity of oil, I'd only hazard a guess, but yeah, we're talking tens of thousands of tonnes."
As more than 80 years of corrosion takes its toll, there is one ship Neil is particularly worried about — USS Atlanta.
"The Atlanta is only 4 or 5 kilometres off Honiara [and] has a couple of thousand tonnes still in it. If there is a major rupture of a fuel cell, that is going to make a big mess," he says.
Marine archaeologist Matt Carter opens his laptop and shows me a satellite map of Iron Bottom Sound.
It's covered in coloured squiggles— more than a dozen of them.
Each squiggle represents an oil slick.
On the map just off the coast of Honiara is one of the biggest— it's USS Atlanta.
"The amount of oil that's coming off that — it's a lot," says Dr Carter.
Dr Carter and his team at Major Projects Foundation have spent the past two years investigating and documenting the corrosion of World War II wrecks elsewhere in the Pacific — Chuuk Lagoon in Micronesia, where a US air raid in 1944 sank dozens of Japanese ships in two days of bombardment.
On his laptop, Dr Carter opens a video of a huge, thick patch of oil trapped on the roof of a wreck in Chuuk Lagoon.
All it would take is for a small hole to appear in the hull – through corrosion, or damage from an earthquake or a tropical cyclone – for it to leak out, potentially releasing thousands of litres of oil into the sea.
Major Projects Foundation is doing something no one else is doing in the Pacific — sending divers down to take tens of thousands of photos of these wrecks in Chuuk Lagoon to create centimetre-accurate 3D models.
"One of the big problems with the potentially polluting shipwrecks is no-one understands what we're dealing with really," says Dr Carter
"By mapping them like this, we can show people, this is what we're actually talking about … and at a technical level we can then go through and we can look at the wreck and we can see areas of damage.
"Then we can get an understanding of which fuel tanks are ruptured, which ones might still be intact, and how much oil it might still hold."
The NGO hopes that once the most "potentially polluting wrecks" are identified, action could be taken to prevent a major spill.
"Across the entire region the wrecks are corroding … and they will release the oil that they have that remains," Dr Carter says.
"The question is how much oil is in these shipwrecks and can anything be done about it before they collapse?"
The wrecks in Chuuk Lagoon are shallower than those in Solomon Islands, making them much more accessible for researchers like Dr Carter.
At the moment, there is no work going on to investigate the ships in Solomon Islands from Japan or the Allies.
Dr Carter says it's not clear who has the legal or moral responsibility to ensure these wrecks don't turn into environmental disasters.
"It's a really complicated situation, but at the end of the day, the Solomon Islanders, the Micronesians, they shouldn't be the ones picking up the cost and being impacted again," he says.
The Japanese embassy in Honiara says they are not involved in any projects relating to oil and fuel in World War II wrecks.
The US Navy did not respond to questions about whether they were doing anything to prevent a spill.
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