HONOLULU — Federal regulators are proposing to ban swimming with dolphins in Hawaii, a move that could imperil one of the Aloha State’s most popular tourist activities and the industry that has sprung up around it.

The National Marine Fisheries Service says spinner dolphins – the playful nocturnal species that humans in Hawaii routinely frolic with – are being deprived of rest during the day and becoming stressed out.

Swimming with dolphins is popular with visitors and some locals, with dozens of companies on Kauai, Oahu, Maui and the Big Island operating dolphin tours daily.

The proposed rule could shut down or disrupt the industry as it now operates. That’s because the ban would cover waters out to 2 nautical miles, which is where 98 percent of Hawaii’s spinner dolphins rest after they’ve spent the night feeding.

Ann Garrett, of the National Marine Fisheries Service, said dolphins have been found to be burning calories at a higher rate because they are forced to be vigilant as people approach their pods.

“All of these things can contribute to a reduction of fitness over time – this kind of chronic level of stress,” Garrett said.

Scientists fear the stress will harm the animals’ ability to reproduce.

The federal agency plans to hold public meetings on the regulations next month and expects to make a final decision next year.

Garrett said Tuesday that the agency aims to require swimmers, snorkelers and others in the water to stay at least 50 yards from the animals.

Spinner dolphins feed at night. At daybreak, they gather in shallow bays for safety.

When they sleep, they rest half their brains and keep the other half awake so that they can surface and breathe. As a result, they can look awake even when asleep.