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.“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."Make sure that they’re comfortable during their visit by giving them space and not disturbing them,” the parks department tweeted.A subsequent necropsy determined the dolphin was suffering from ailments that weren’t linked to the notoriously filthy Superfund site."