After Mayor Kirk Caldwell’s stay-at-home executive order aimed at curbing the spread of the coronavirus pandemic went into effect March 23, Scotty Nelson smiled as he carried his surfboard through Makalei Beach Park near Diamond Head to paddle out to the break known as Suis.

“We’re so lucky we can get out in the water,” Nelson said, noting that in Honolulu, where all city parks are closed under the order, people are still allowed to cross city beach parks to access the ocean.

Two weeks later, surfers’ luck still held: “You can go to the beach to exercise quickly (or) gather limu and go home,” the mayor said in a news conference Tuesday, adding that jogging, walking, swimming and surfing at the beach were permitted, “but sitting on the beach, lying on the beach, close to each other,” was not.

Honolulu police so far have issued more than 5,000 warnings and 353 citations and made 26 arrests for violations of the order, including for gatherings of 10 people or more, “mostly at the beach parks,” Deputy Chief John McCarthy said at the news conference.

>> PHOTO GALLERY: Tuesday scenes around Oahu during Hawaii stay-at-home mandate

In California most beaches are closed and surfing is prohibited, but while driving to work, scientist Kim Prather, a professor at the Scripps Institution of Oceanography in San Diego, said she saw “people were still congregating at the beach” and decided to warn the public about the coronavirus’ potentially longer reach out of doors.

Prather, who specializes in tiny aerosol particles smaller than 5 micrometers in diameter, including viruses, said outdoor exercise such as surfing, swimming, running and bicycling can propel virus particles farther than the recommended 6 feet of social distancing.

And at the beach, “where it is breezy, 6 feet might not be enough” even if people are just walking or standing still.

The World Health Organization’s website says SARS-CoV-2 is spread by larger, 5- to 10-micrometer droplets in coughs and sneezes that don’t generally travel beyond 6 feet, but aerosol experts warned recently in the journal Nature that the coronavirus also could travel through talking and breathing.

With an estimated 25% of coronavirus cases showing no symptoms, someone can be infected and not know it, Prather said, and “it is possible they will breathe out (infected) aerosols, which can be carried farther distances.”

How far? “The best analogy is how far you move away from a smoker if you don’t want to inhale the smoke,” Prather said.

Steven Howell, a research faculty member in the Department of Oceanography at the University of Hawaii at Manoa, agreed.

“If you are within cigarette-smelling range of someone, you’re also within range of any SARS-CoV-2 they are breathing out,” Howell said.

“When I’m talking with someone outside, I try to have neither of us downwind from the other,” he added.

Prather’s research has also shown that some other bioaerosols, including bacteria and viruses, can enter ocean air from sewage.

She said more research is needed to determine whether this can happen with SARS-CoV-2 and whether it loses infectiousness through sewage treatment and exposure to air, sunlight and water.

But she wanted to clarify that in an April 2 article in the Los Angeles Times, “when I said I would not go in the ocean, I was talking about where sewage is pouring in,” Prather said. She said she was referring to the presence of pathogens carrying waterborne disease after sewage spills or heavy rain, and was not saying that SARS-CoV-2 was known to be waterborne and posed a threat to surfers and swimmers.