The incident occurred in the coastal Dutch town of Zandvoort, west of Amsterdam, on Tuesday (19 July), and footage shows the topless woman clambering on to the back of the creature as onlookers urge her to stop.
Police opened an investigation after reviewing the video and the woman has since handed herself in, according to RTL Nieuws.
Annemarie van den Berg, of aquatic mammal rescue organisation SOS Dolfijn, told RTL Nieuws that it was ‘very disturbing’ to see the long-beaked dolphin in this environment.
She said: “If they end up in the North Sea, they get into trouble. These animals do not survive well in these types of waters. They look for food at a depth of two to three kilometres.
“If that happens [they get stranded], they are doomed. Our goal is to have the animals turn around so that they swim out of the North Sea on their own.”
As police investigate the incident, they have urged the public not to send the woman abuse online.
They said: “We understand that this story evokes emotions. That should never be a reason to make threats on social media. This is also punishable. Therefore do not do this.”
Swimming with dolphins is of course a fairly common holiday activity these days, and the creatures are admired for their intelligence, inquisitive nature and elegance in the water.
She and her husband Steve were on a cruise to celebrate their 40th anniversary, alongside their kids and grandchildren.
The couple, from Acushnet, Massachusetts, had planned a number of excursions, including a swim with dolphins, as their cruise made its way to a number of Caribbean islands and Mexico.
All seemed to be going well until she waited for the two dolphins to swim behind her for the ‘dolphin tow’. At this point, one of them rammed her in the lower back, before striking her another two times.
Janet told Boston 25 News: “Maybe two seconds after that hit, here comes another one.
“It’s like somebody would take a baseball bat, like David Ortiz would take a baseball bat and just swing it at my back.
“You start thinking, ‘If this hits me one more time, I could die,’ die in front of my family and in front of my three young grandchildren.”
Janet sustained a broken spine and ribs in the attack, and it took more than a month for her to get back on her feet.