A bullet in the mail, an anonymous phone call and a secret map showing the dump site – it's a case full of intrigue and suspicion. But what's the truth behind claims that drums of deadly poison have been buried by a South Island dam, in a lake used for recreation and fishing?
For decades they've dipped their lines, dangled their lures – simply enjoyed the river.
"If you wanted to have a drink you would drink out of the river," says Temuka's former pharmacist, Allan Campbell.
"We'd just go over to the river here, five minutes' walk, and catch 10 trout and be back in half an hour," says community man Ray Brokenshire. "We're angry ratepayers that aren't getting what's better for our rivers."
"What is going on is appalling," says environmental chemist Nick Wall.
These small-town eco-warriors, members of the Opihi Catchment and Environment Protection Society (OCEPS), won't abandon their belief that the waterway has turned toxic.
"I wouldn't drink out of this s**thole, no," says Mr Campbell.
The water comes from Lake Opuha. Manmade and farmer-owned, the irrigation storage dam is filling up now.
It ran dry for the first time this summer and its cracked and broken bed threw up some dirty secrets.
Whispers that something more serious, more sinister is buried beneath have dogged the dam for years.
In 2011, a former labourer-turned-whistleblower claimed that during construction drums of banned agrichemicals were dumped there.
The author of the affidavit is now elderly, frail and in poor health. His family was reluctant to grant access, but over the phone he said, quite firmly, that he stands by his statement. He said he was told to forget what he'd seen and the drums were buried.
Up until it was banned in 1989, DDT was a widely used insecticide. Many farmers, and others, were left with ample stocks in their possession.
Environmental chemist Grant Northcott specialises in organic contaminants.
"High residues of DDT has been linked to increased incidences of breast cancer and obesity and the incident of diabetes," says Mr Northcott.
Canterbury's regional council, Environment Canterbury (ECan), followed up on the whistleblower's claim by testing water, sediments and fish from Lake Opuha. It found nothing out of the ordinary.
But our three campaigners claim the scientists weren't testing in the right place. They say they now know exactly where the chemicals were allegedly dumped; they have the GPS coordinates.
"I receive a phone call from a withheld number, and he said to me, 'I have confirmation of where that dump site is. Have a look in your mailbox in two hours' time. There'll be GPS marking everything to get to it,'" says butcher Barry Stone. "I still don't know who he was."
So with map in hand, they met up at the dry lake with an (ECan) employee to walk through the marked locations. The decision was made to send in a ground-penetrating radar. The men say they were told they'd be involved, but it went ahead without them. Again, nothing was found.
"Sediment samples were taken in 2011, not when we were doing the underground radar, because that was when we were trying to find the location of a dump," says ECan CEO Bill Bayfield.
Frustrated that not a single sod had been turned or tested, Mr Campbell, Mr Brokenshire and Mr Stone decided to dig themselves, dig for buried traces of pesticides and insecticides.
They took their jars of mud to a South Canterbury scientist.
"We have found DDT, its metabloytes, chloro-pesticides," says Mr Wall.
Now firmly in the OCEPS camp, Mr Wall is an international environmental chemist with what he regards as a state-of-the-art testing kit – high-performance liquid chromatography with tandem mass spectrometry.
But he won't show it. Following threats, including a graffiti attack on his property, Mr Wall does not want to divulge to anyone his secret laboratory location.
"I will stand by the science and I'm quite prepared to have it peer-reviewed by anybody. They can come down and they can see the results."
Sediment samples from the lake bed were sent to laboratories here and overseas. We asked our expert to review the results.
"Certainly the highest concentrations I've seen in freshwater or marine sediment in New Zealand," says Mr Northcott.
"They're staggering," says Mr Bayfield. "They're very, very high."
So what do the figures mean? How much DDT is too much?
If you live in suburbia, proposed soil contaminant guidelines state levels can't exceed 70 parts per million. In playing fields and parks it's 400 parts per million.
But what they claim to have found at Lake Opuha far exceeds any safe limits.
The DDT concentrations across all laboratories average as high as 6000 parts per million. So if the results ring true, how safe is the vast body of water, the water that leaves it and water drawn downstream, from river aquifers to supply the people of Timaru?
"I'm very, very pleased the TDC moved very rapidly to sample their water supply," says Mr Bayfield. "I'm satisfied at this stage that for water users, which of course is potentially the people of Timaru, it has no risk at all."
"If you test water you're never going to find it," says Mr Wall. "Test the sediment and you will find it, so if you have flood events which bring sediment down the river, chances are you're bringing these fluoro chemicals down the river with you."
He claims his soil sampling downstream shows that's already happened.
"What is the long-term effect on our health, our immune systems? Nobody knows," says Mr Campbell.
"I guess now that Mr Campbell's got some results I'm confident that we're going to move really fast and really hard to work with them to find out just real this risk is," says Mr Bayfield.
Right now, neither party has faith in the other's integrity. ECan has cast doubt on the sampling process; the men are adamant they've done it all by the book, and they'd like to know why a rubbish tip was not cleaned up as ECan promised.
Then there are those directly affected by allegations of buried toxic waste, the hundreds of people who need the dam to draw a livelihood.
Tensions are spilling over.
"A couple of farmers came into the pharmacy I had in Temuka and basically told me, 'You buggers better not have found anything,'" says Mr Campbell.
"Receiving a live bullet through the post saying, 'The next one's for you,'" says Mr Wall on a threat he received.
Mr Brokenshire has been advised not to go fishing in the back country alone. Mr Stone was also warned off after he presented at a public meeting.
"I know nothing and that's very unfortunate if it's that, and I guess that just reflects the importance I guess that this is seen within the region, but any behaviour like that is totally unwarranted," says Opuha Water Ltd CEO Tony McCormack.
The dam company, the self-proclaimed river guardians, the regulatory authority – what everyone is in agreement on is that 17 years of simmering discontent over what might lie at the bottom of this lake must be put to bed once and for all.
"It's expensive, it's time-consuming, but with DDT it's necessary," says Mr Bayfield. "There's a real risk here and we accept that."
"I'm sure the problem can be solved," says Mr Campbell. "We would like it to be solved so that the health of our kids, grandkids, future generations can be assured."