There’s one upside to the Big Apple’s summer solstice rainstorm: a temporary waterfall in Mt. Prospect Park!

Heavy rain caused a stream several inches deep to gush down a staircase at the park on Friday — creating a mini-Niagara Falls.

The downpour turned the park’s staircase entrance at Eastern Parkway and Underhill Avenue into a wild spectacle, stunning morning joggers and dog walkers who paused to soak up the nature-in-the-city moment. Other Brooklynites laughed and snapped photos.

Earlier in the day, flash flooding prompted a state of emergency upstate and in parts of New Jersey, according to Accuweather.com.