Dolphins make a splash in New York City's Bronx River

A bystander captured video of dolphins in the Bronx River this week, the first time the animals have been seen in the river since 2017. (Courtesy Nick Banco)

Dolphins are swimming their way back to New York City's Bronx River for the first time in over five years.

On Monday, a pair of dolphins were spotted in the river, which flows through southeast New York, according to the New York City Department of Parks and Recreation. The department posted a video of the cetaceans bobbing through the water at Starlight Park on Twitter.

"It's true—dolphins were spotted in the Bronx River this week!" wrote the department. "This is great news—it shows that the decades-long effort to restore the river as a healthy habitat is working. We believe these dolphins naturally found their way to the river in search of fish."

The department encouraged New Yorkers to "welcome these dolphins to the Boogie Down."

But despite how tempting it might be to get a closer look at the aquatic animals, the department also advised spectators to "make sure that they're comfortable during their visit by giving them space and not disturbing them."

This is the first time dolphins have been seen in the Bronx River since 2017, the department told CNN over email. Dolphins were spotted in the East River as recently as last year.

The department explained it restocks the river with alewife and other fish, which likely attracted the dolphins.

The Bronx River Alliance, a nonprofit that works to protect and restore the river, also confirmed the sightings on social media.

"There seems to be more dolphin pods swimming near NY Harbor!" wrote the nonprofit. "We are not sure why but authorities are further investigating their presence and we will keep you updated as we get more info."

Bottlenose dolphins are found off both the West and East Coasts as well as in the Gulf of Mexico and in the Caribbean, according to the National Oceanic and Atmospheric Agency. The species are protected throughout the nation under the Marine Mammal Protection Act, which makes it illegal to feed or harass the animals. They have faced population decline due to habitat destruction, pollution, and entanglement with fishing gear.