Mystery continues to surround the the two-headed fish larvae at Gwen Gilson's Sunland Fish Hatchery, which came to national attention this week after 90pc of her latest batch of embryos, taken from breeding stock from the Noosa River, emerged deformed, including some with two heads.

But Ms Gilson said the problem wasn't a new one and claimed it was clear to her what was causing it: chemicals from an adjacent macadamia farm.

She and NSW veterinary expert Dr Matt Landos made a video to explain what they thought the impact from the chemicals were, including reducing the catch from the Noosa River and causing health effects in people.

"Over two years ago, we noticed that after the spraying drifted over our ponds, our next batch had convulsions and every time we have used water that has been exposed to the (Carbendazim) spray, we have the same results," Ms Gilson said.

Ms Gilson said that ever since, she has had problems with contaminated water on the site affecting the hatchlings.

"This time, we went to the river to get wild stock and this has happened.

"We still can't use the water from the site and can only get normal births by using water from our other site or treating them with atropine."

Carbendazim products are used for the control of mould, spot, mildew, scorch, rot and blight in a variety of crops including cereals, fruit (pome, stone, citrus, currants, strawberries, bananas, pineapples, mangoes, avocados), as well as macadamia production.

Australian Macadamia Society CEO Jolyon Burnett said no other cases like this had been reported near macadamia farms and the chemicals used by farmers were thoroughly regulated.

"Macadamia farmers often have their families on the farm and they wouldn't spray anything that would have serious health effects on their children," he said.