"Next thing the medium-sized dog came hurtling towards me. The guy yelled out 'don't worry, he won't hurt you', so I let my guard down. The dog then attacked me, biting my lower leg and ankle.
"Luckily I had track pants on and there was a zip where the dog latched on to my leg.
"If I'd been wearing shorts it would have been a lot worse - there's a lot of things like tendons that can get damaged in that area.
"The owner was really apologetic and horrified and put the dog in the car."
Mr Spain went to the emergency department at Whanganui Hospital where he was treated for two large puncture marks and a laceration down to the bone on his lower left leg. The wound was too deep to be stitched because of the risk of infection.
"I was horrified when they said at A&E that this sort of thing is quite common. We moved from Rotorua to Whanganui five months ago and I had no idea there were so many dogs here or that dog attacks are at alarmingly high levels.
"There are families and children on the beach. We often take our own grandchildren.
"What if a dog attacks a child or if my grandchildren had seen what happened to me and been traumatised?
"There should be a bylaw that all dogs are muzzled or on a lead in public areas. The council needs to do something proactive about it before something serious happens to a child."
Council compliance team leader Warrick Zander says animal control has impounded a dog he suspects was involved in the attack on Mr Swain.
Mr Zander said the dog, an unregistered male mastiff cross, has previously come to the animal control team's attention for rushing.
A decision about the dog and any prosecution of the owner will be made when an investigation is completed.
"In any public area, whether it is a designated dog exercise off-leash area or in a public place, owners must be able to control their dog either on a leash or, if off-leash, through voice or hand commands," Mr Zander said.
"Owners must also be able to see their dog at all times. Controlling your dog also means not letting it rush up to say hello to a stranger or chase birdlife, no matter how friendly it is.
"If a dog is seen running free in a leashed area, especially when it is causing a nuisance to other animals or to people, we ask people to please contact the animal management team."
Mr Zander said the council's dog-control handbook has more tips for keeping dogs under control.
Dogs classified under the Dog Control Act as menacing or dangerous must be muzzled in a public place, he said.