"As soon as you pull it up and cut into it, it just wreaks of mice," said Wagga-based fisherman Craig Harris.

"There's three or four mice in each fish, that's just yuck. A lot of people have said to me when they come to eat it, it just wreaks of dead mice."

The worst of the situation is being felt in the west Murrumbidgee River system, where the mice continue to be in greater plague proportions.

"We haven't seen anything like they've seen out there," Mr Harris said.

"It just means [fewer] people will be harvesting fish at the moment because you really can't eat them."

Rod Cockburn from the Compleat Angler in Wagga, said it was a situation that will likely get worse, but which is not uncommon.

"Fish will eat mice, fish will eat anything that falls into the river - birds, mice, rats, anything," he said.

"Majority of the cod will be feeding on mice right now. They'll eat whatever is in front of them.

"Trout will also feed on mice, and yellow bellies would too. It's natural, it never surprises us."

At the moment cod is in such abundance that a short fishing session can bring up as many as 20 fish.

But, Mr Cockburn and Mr Harris agree, few will harvest more than one and especially so at the moment.

"It's just the reality even when there isn't a mouse plague, you'll catch them and they may have eaten a mouse," Mr Cockburn said.

"I pulled up a fish years ago that had just eaten a water rat and it regurgitated it up. Stunk like anything, but it is natural."

With the Murray Cod so dependent on a mouse diet, it has brought up concerns for the health of the river system during widespread baiting.

Healthy Rivers spokesperson Mel Gray told AAP the NSW government's mission to roll out bromadiolone was cause for worry.

The rodent poison was described by Agriculture Minister Adam Marshall as being "the equivalent of napalming mice", and will form part of the $50 million government package to deal with the plague.

"If he thinks it is was going to napalm mice, well he better be prepared for the consequences of napalming vulnerable Murray Cod as well," Ms Gray said.

Charles Sturt University environmental sciences expert Dr Maggie Watson has also spoken of the dire effects the poison will have on rodent-eating birds of prey.

"It's what we call 'top-down control'. They [the birds] keep control of the insects, smaller bird, and marsupial populations. Basically, they keep a lid on the populations of everything beneath them," Dr Watson said.

"If you remove them from an environment, other populations go out of control and you'll have more frequent locust and mouse plagues."

A spokeperson for the NSW Department of Primary Industries (DPI) said that the impact of poisons on the waterways would be monitored going forward.

"Regular fishers will know Murray Cod and Golden Perch often eat mice that fall into the water," the spokesperson said.

"When mice are in plague proportions you find that cod in particular will switch on to them, they'll become more aware of mice as a food source because there are more mice present.

"The key point in terms of managing the impacts of any bait or poison is to ensure it is applied and managed in way that will minimise any secondary impacts.

"Any mice affected by bait would be in and around crop perimeters and so are unlikely to be the mice being eaten by fish."

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