The Chair of Water Safety Ireland in Waterford says there's very little people can do to avoid the weever fish except staying out of the water at low-tide.
There have been reports of several people in Waterford stepping on the sandy-coloured fish while swimming in recent days.
Lola O'Sullivan says the pain is excruciating as the spines embed into your foot and discharge their poison.
"The pain is at the worst for about the first two hours. You don't generally see the fish so you just feel this dart of pain usually that goes into the foot.
"If you're in a lifeguarded beach, go straight to the lifeguards and they will treat you by placing the affected area in warm water and gradually heating the water as hot as the person can bear over a 20-30 minute period."
She added that "this increases the blood flow and assists the natural healing, the heat helps to break down the poison".
Lola O'Sullivan says you can apply this treatment yourself but "it should be treated swiftly to reduce the pain".
"If the pain does not reduce after two to three hours you should attend your doctor.
"Weever fish are very common in Irish waters, there is nothing you can do to avoid them other than not going into the water when the tide is low."
