Dolphins have been spotted swimming in the Bronx River, the parks department tweeted on Thursday, touting the sighting as a sign of the city’s healthy waterways.

Instagram user nick_banko first shared a video of the dolphins frolicking in a section of the river near Starlight Park on Monday.

“Alright now I need some answers,” his caption read. “If you from the Bronx and know this park, somebody please explain to me why tf is there dolphins in the f---ing park.”

The parks department then shared his video and explained that the dolphins’ visit was a good thing.

“This is great news — it shows that the decades-long effort to restore the river as a healthy habitat is working,” the tweet read. “We believe these dolphins naturally found their way to the river in search of fish.”

Wildlife Conservation Society scientist Howard Rosenbaum said the dolphins in the video were “common dolphins” that appeared healthy and not in distress.

“We've come a long way across multiple decades of environmental improvement, water quality cleaning, better environmental stewardship, better relations, all of which helps the overall environment and then leads to recovery of these systems,” he said. “I think it's just great that these things are happening and hopefully the overall environmental recovery for these urban waterways continues, and we continue to see marine wildlife – their habitats, their prey – flourish."

Assemblymember Kenny Burgos, whose district covers the park, joked about clearing his schedule to go dolphin-watching.

The Bronx dolphin sighting wasn’t the only one in the city this week. The Newtown Creek Alliance shared a separate video on Instagram of two dolphins swimming in the toxic waterway north of Greenpoint, Brooklyn. It was unclear if they were the same dolphins spotted in the Bronx.

“We encourage you to welcome these dolphins to the Boogie Down! Make sure that they’re comfortable during their visit by giving them space and not disturbing them,” the parks department tweeted.

The agency’s lighthearted tone was a notable departure from 2013, when a dolphin swam into the Gowanus Canal and died. A subsequent necropsy determined the dolphin was suffering from ailments that weren’t linked to the notoriously filthy Superfund site.

Updated to add comment from Howard Rosenbaum.