While swimming with dolphins is a popular tourist activity, it is against federal law to swim within 50 yards (45 meters) of spinner dolphins in Hawaii’s nearshore waters.

The prohibition went into effect in 2021 amid concerns that so many tourists were swimming with dolphins that the nocturnal animals weren’t getting the rest they need during the day to be able to forage for food at night.

The rule applies to areas within 2 nautical miles (3.7 kilometers) of the Hawaiian Islands and in designated waters surrounded by the islands of Lanai, Maui and Kahoolawe.

Enforcement officers at Hawaii’s Department of Land and Natural Resources came across the 33 swimmers in Honaunau Bay on Sunday during a routine patrol, they said today.

The National Oceanic and Atmospheric Administration (NOAA) banned tourists from swimming with spinner dolphins in 2021.

It came into force after biologists noticed that the playful mammals were becoming stressed by human interactions.

The nocturnal animal is known to frequent the waters close to shore during the day while they rest.

The rule applies to areas within 2 nautical miles (3.7 kilometers) of the Hawaiian Islands and in designated waters surrounded by the islands of Lanai, Maui and Kahoolawe.

Shocking aerial footage shot by drone shows over a dozen snorkelers appearing to hound the dolphins as they swim away and disperse.

The department said its video and photos showed swimmers ‘who appear to be aggressively pursuing, corralling and harassing the pod.’

Officers contacted the group while they were in the water, and told them about the violation.

Uniformed officers met the swimmers on land where state and federal officials launched a joint investigation.

Hawaii´s spinner dolphins feast on fish and small crustaceans that surface from the ocean´s depths at night. When the sun rises, they head for shallow bays to hide from tiger sharks and other predators.

To the untrained eye, the dolphins appear to be awake during the day because they are swimming.

But because they sleep by resting half of their brains and keeping the other half awake to surface and breathe, they may be sleeping even when they are maneuvering through the water.

Hawaii’s Division of Conservation and Resources Enforcement (DOCARE) and the NOAA Office of Law Enforcement are investigating, according to the statement.

It comes after officials on the Aloha State earlier this month announced a similar investigation into a man who refers to himself as ‘Dolphin Dave.’

The man from Maui was caught repeatedly harassing a humpback whale and a pod of dolphins during a snorkeling trip.

He has been identified as 65-year-old David Jiménez, and was allegedly seen snorkeling close to a humpback whale in Kealakekua Bay State Historical Park on Sunday, DLNR said.