Deana Brown spotted an adder on the sand in Porth Neigwl, Wales, over the bank holiday weekend and urged pet owners to be careful.
She posted a video of the encounter online and told North Wales Live that she hoped it would “stop a dog or a child being bitten”.
It comes after experts advised that warmer weather in the coming months could see the risk of snake bites increase.
One pooch, Florence, was bitten in Southend, Essex, last month and carers at Medivet said that they fear similar incidents may occur.
Medivet posted on Facebook: “This gorgeous Italian Spinone is Florence she unfortunately had a run in with an Adder and received a bite. This occurred yesterday evening over at Benfleet Downs near the car park.
“As you can see from the second photo, the bite occurred on Florence’s leg and caused swelling. You also see the puncture mark.
“You may remember seeing a similar post a couple of weeks ago about another patient we had that received a snake bite.”
And the firm urged: “As it starts to warm up, Adders will start to emerge from hibernation so be especially careful of walking dogs in known adder areas and in areas of long grass where your dog might stumble across one.
“If you suspect your dog may have received a bite from an adder, please call us.”
The RSPCA and other charities have highlighted a surge in the spread of Britain’s abandoned snakes and other exotic pets.
Up to 100 adder bites on humans are reported each year – and the NHS says victims should dial 999 or head to A&E if afflicted, though the bites are rarely fatal.
The last person to die of an adder bite in the UK was in 1975 when a five-year-old boy was attacked in Scotland.
But an eight-year-old girl had to be rushed to hospital a year ago after being bitten by an adder during an Easter picnic with her family in Staffordshire.
It’s estimated that the UK has more than half a million legally-owned snakes – along with 400,000 lizards, most commonly bearded dragons and leopard geckos.
Adders also bite around 100 dogs each year and symptoms can include swelling, vomiting, drooling and breathing difficulties.
Meanwhile, pet owners were given another expert warning over the fact that tap water could be “slowly poisoning” their furry friends.
Likewise, a vet recently raised the alarm about a number of common garden hazards that could make pets seriously ill.