The discovery of more than a dozen dead cows left floating in a New South Wales North Coast river for at least 10 days has sparked concerns about increased shark activity and risks to public health.

The State Emergency Service (SES) was initially called in following reports a number of cattle had become stranded at the bottom of a steep river bank in the Richmond River.

Warning: This story contains images that may be disturbing for some readers.

SES Lismore branch member Neville Graham said it had been a distressing situation.

"The cattle that weren't able to be saved appeared to have been there for some time," Mr Graham said.

"There are bull sharks that go up the river, so once they get a bit of sniff of something available like that, I'd say the bull sharks would probably be frequenting the area as well.

"We were able to save three of the animals and tow them to somewhere they could get out of the water.

One of 13 dead cows left floating in the Richmond River for at least 10 days after becoming stranded. ( Supplied: Phil Terry )

"The fourth one was probably going to be euthanased anyway. We were allowed to at least try to save the animal, but it just didn't make the distance."

Mr Neville said it was not part of the SES charter to remove dead animals from the water, and the onus laid with the property owner or the council.

Local man Phil Terry said he was appalled to see 13 dead cattle still in the river between Lismore and Coraki on Sunday.

Mr Terry said there had been children jumping into the water nearby and people fishing.

"For a moment I thought 'Right, are we in the Ganges?' But then I think about the Indians and they worship their cows so they wouldn't let this happen," Mr Terry said.

"We don't let this happen to cows that are travelling by boat to Indonesia.

"These cows have suffered completely. They've fallen in the river, they're stuck in the mud, [and] they're in the middle of the river."

The RSPCA has told the ABC a water pump had failed on the property, and the cattle became stuck after making their way down a steep bank to drink.

It is investigating the issue.

One of 13 dead cows seen floating in the Richmond River between Lismore and Coraki. ( Supplied: Phil Terry )

Greg Bell, from the North Coast Public Health Unit, said micro-organisms escaping from the rotting cows could cause eye, ear or stomach irritations to people swimming or taking water from the area.

"The longer that the carcasses are left there, the more that they actually break down naturally, so the concentration of various bacteria and micro-organisms will naturally get worse," Mr Bell said.

The ABC has approached the Lismore City and Richmond Valley councils for comment.