Goulburn-Murray Water has sought to reassure irrigators in the Cohuna area after announcing it is using a herbicide first used in 1960 to clear aquatic weeds from channels in the area.
GMW has told irrigators it will be using Acrolein to clean out weeds in the Cohuna channels, after an increase in weed infestation since August last year.
"Water for irrigation during this time will be safe and available for use but there will be a non-water use period of 72 hours for stock and domestic purposes," GMW distribution assistant manager Tim Nitschke said.
"This means water during this 72-hour period is not recommended for consumption by livestock."
The chemical, which has been in use since 1960, broke down into water and carbon dioxide within 72 hours.
He said irrigators should prepare any on-farm storages, or any other measures appropriate to their properties.
In GMW channels, submerged aquatic weeds such as ribbon weed, egeria, elodea and pond weeds could impede water flow, cause erosion and may cause it to run over the banks.
GMW has advised property owners Acrolein would be used "very sparingly" and as a last resort to treat the weeds.
It has confirmed it is toxic to aquatic life and it was possible fish and yabbies may die as a result of the treatment.
But Cohuna dairy farmer Jodie Hay said she was concerned about the way GMW was communicating with irrigators.
"There are some dramas about how they are communicating with us; it's by mail, which is fairly hit and miss," Ms Hay said.
I am nervous about whether we are going to be notified correctly, or how are they going to know everyone has been notified.
- Jodie Hay, Cohuna dairy farmer
"When we are ordering water, we do it by text message, I think that would be a more sensible approach."
She said some properties no longer had dams, as water lines ran straight to the channels.
"What other water sources do you have when it's 40 degrees?" she said.
"I wonder if it's time to look at different ways of treatment.
"They have modernised the channels and they have things like the fish screens, which are supposed to stop fish going into the channels, so they don't get stuck in a one-way system."
She said she was also concerned about the withholding period for water used to irrigate pastures, used to produce milk.
"I am nervous about whether we are going to be notified correctly, or how are they going to know everyone has been notified," she said.
Cohuna hobby farmer Vicky Johnson said she was concerned about the impact on the environment, particularly as Acrolein was toxic to fish, yabbies and frogs.
GMW had confirmed the herbicide was toxic to marine life.
Ms Johnson said she had been told previous use of Acrolein had killed fish and yabbies.
"One man I talked to can remember all the yabbies crawling out of the channels, and all the dead fish," she said.
"They were cleaning them up for weeks."
Ms Johnson said one solution might be to return to dropping the level of Gunbower Creek, which supplied the irrigation channels.
"Since modernisation Gunbower Creek has become a water carrier to flood the bush," she said.
"They don't drop it (reduce the flow) anymore, and as a result, the weed has just grown.
"They used to drop it in winter, to kill off the weed, and it also helped harden up the banks."
Ben McInnes, who runs beef cattle in the area, said weeds were clogging up the creeks in the area.
"We have been on the creek all our life, and it's in the worst condition it's been in," Mr McInnes said.
He was not concerned about the use of the chemical.
"If they put it in and clean it up, good on 'em," he said.
"In some spots, it's choking up the pumps and foot valves.
"It's growing in the shallow water and creating more silt."
In an attempt to alleviate the concerns of locals, GMW has communicated to residents likely to be affected Acrolein has been used for the control of submerged weeds since 1960.
"Currently there are no alternatives to this product in Australia," GMW said.
"However GMW and other agencies are attempting to register alternative herbicides."
Water could still be used for irrigation, during the withholding period.
An exact date for the herbicide application had not yet been determined.
The date would be dependent on the short-term weather forecast.
GMW had notified customers in the area of plans for the treatment and would provide at least three days' notice, when a date for the herbicide application was confirmed.
When planning herbicide treatment in the channel system, GMW has also worked closely with relevant agencies - including Catchment Management Authorities (CMA), Victorian Fisheries Authority and the Environment Protection Authority - to ensure the application was conducted in a controlled and safe manner.
Operational planning for herbicide injections could include electrofishing.
GMW had engaged a specialist with the CMA to use electrofishing as part of the treatment, to net as many fish as possible and move them out of the channel to be injected with the herbicide.
As part of its winter works program GMW was looking to other strategies for weed treatment.
This included de-watering channels during the irrigation shut down.