For months, Sallomé Hralima and her two young daughters watched as a fire hydrant in their neighborhood was transformed into a destination in Brooklyn.

What started as a pool of water around just another gurgling hydrant in Bedford-Stuyvesant flourished into a small ecosystem when local residents brought in goldfish. Then came benches, a lending library for books and toys and décor. The hydrant even got a Google Maps designation: the Brooklyn Aquarium.

“It’s on our way to the park, to the grocery store, to the bus, to the train — we see it nearly every day and we always stop,” Ms. Hralima, 44, said. “It was constantly changing, so we would go look to see what had been added.”

The aquarium, as residents called it, was “a conversation piece” in the neighborhood, she said.

But on Friday morning, when Ms. Hralima woke up early to run to the grocery store, she discovered a very different scene. The city’s Department of Environmental Protection was removing the fish, the colorful pebbles and even the fake fauna of their little oasis, and paving over the pond.

In a statement, the city agency said the move came after a fire department inspection found the hydrant to be leaky, which put it at risk of freezing and becoming inoperable. A lock was installed to prevent it from leaking further, and new concrete was poured to “ensure pedestrian safety,” it said.