Tourists flock to Hawaii every year to swim among spinner dolphins, a rare chance to get a glimpse of these incredible and intelligent animals up close.

But authorities have proposed to ban the activity, saying that snorkelers are “disturbing” their daytime habits of relaxing, playing and even swimming when they are asleep, “causing a departure from natural behavioural patterns that support the animal’s health and fitness”.

The National Marine Fisheries Service of the National Oceanic and Atmospheric Administration has proposed that people cannot swim within 50 yards of the dolphins.

The new rules would affect tour groups that approach the animals by boat, before people jump in the water and swim towards them.

“We think by identifying 50 yards as the minimum distance that there still can be a viable tourist industry in Hawaii,” said Ann Garrett, an assistant regional administrator for protected resources for the National Marine Fisheries Service, as reported by the New York Times.

Tour operators disagree that swimming with the animals impacts on their ability to breed or to feed at night.

Melainah Yee, owner of Sunlight On Water in Kailua-Kona, was one of the first tour guides to take groups out on the water 20 years ago, along with her husband, Michael Yee.

Her company guides a group of between 20 and 22 people every morning for a four-hour tour, and how long they swim in the water depends how quickly they scout dolphins.

"The main two things that we share with our guests is no aggressive swimming - we put our arms are by our sides or behind our backs - and we kick with our fins," she told The Independent.

"It depends what the dolphin does, but we don’t want to swim at them, we want to swim with them. We don’t try to touch them or cause them any harm."

Authorities first brought up the 50-yard proposal in 2006, and have re-introduced it a decade later, she said.

Members of the public have 60 days to comment on the rule, which will probably be decided within a year.

The Marine Mammal Protection Act already forbids people from harassing dolphins, but the 50-yard rule is new, and applies to coastal area within two miles of the Hawaiian islands.

Ms Yee said that spinner dolphins are a smaller breed and it would be "almost impossible" to see them, let alone swim with them, from 50 yards away.