Federal authorities are investigating a group of swimmers who were caught on camera allegedly harassing a pod of dolphins on Sunday in violation of federal law, officials announced this week.

A drone video deployed by officers with the Hawaii Department of Land and Natural Resources caught the 33 swimmers allegedly “aggressively pursuing, corralling, and harassing the pod” in Hōnaunau Bay on Sunday morning, officials announced Tuesday.

The 39-second clip the agency posted online appears to show over a dozen of the swimmers pursuing 11 dolphins. The dolphins eventually split off into two directions in the waters, and some of the swimmers turn around and appear to stop pursuing some of the dolphins.

The allegations could put the swimmers in violation of the Marine Mammal Protection Act, a law enacted in 1972 that makes it illegal to harass wild marine mammals, including dolphins, whales, seals and sea lions.

The act stipulates two levels of harassment, according to the National Oceanic and Atmospheric Administration: one referring to “any act of pursuit, torment, or annoyance” that could injure a marine mammal, and another referring to “acts that have the potential to disturb (but not injure) a marine mammal” by disrupting their breeding, feeding and other routines.

The spinner dolphins involved in the Sunday incident are also protected by a specific rule published in 2021. It prohibits swimmers and vessels from coming within 150 feet of the dolphins within two miles of the Hawaii shoreline, according to Katie Wagner, a NOAA spokesperson.

Spinner dolphins — smaller members of the species known for leaping and spinning out of the water — may be sleeping even when they appear to be awake and moving through the water, the Associated Press reported. That’s because half of their brains remain “awake” while they swim, helping them to breathe and remain on the surface of the water.

NOAA warns that disturbing spinner dolphins could disrupt their daytime rest, negatively impacting their health and reproduction and leading them to become aggressive or avoidant.

Officers with the Hawaii agency’s Division of Conservation and Resources Enforcement, who were conducting what officials described as a “routine patrol” in the area, deployed the drone after spotting the swimmers from land on Sunday, Hawaii DLNR Senior Communications Manager Dan Dennison said.

The officers alerted the swimmers to the alleged violation while they were still in the water and then met them on land, where they initiated a joint investigation alongside the NOAA Office of Law Enforcement, according to the news release.

The swimmers have not been publicly identified.

It was not immediately clear what kind of penalties the swimmers could face — though NOAA guidelines say people prosecuted in violation of the Marine Mammal Protection Act could face civil penalties of up to $11,000 and up to a year in prison.

Officials urge people to observe wild dolphins from a distance of at least 150 feet by land or sea and to avoid circling, entrapping or swimming with them, NOAA guidelines state.