Google parent company Alphabet is testing the balloons in Nevada.
One of Google’s internet balloons, also called Project Loon, was spotted over Yellowstone National Park last week. The balloon was first spotted by aviation researcher Jason Rabinowitz, and also reported by ReCode.
Project Loon, which is a division of the Google parent company Alphabet’s goog moonshot factory, aims to provide internet connectivity to remote areas of the world that don’t have access to an internet signal. The organization uses huge balloons to create a wireless network in the sky that can beam the web down in places that lack stable high-quality Internet connections.
The balloons themselves are essentially a network of solar-powered, airborne cell towers floating at a height between 60,000 to 90,000 feet, or roughly twice as high as planes fly. The network draws its own connectivity from ground stations and passes it on balloon-to-balloon. People then connect to the balloon using a phone or other 4G/LTE-capable device.
Get Data Sheet, Fortune’s technology newsletter.
In February, the nation of Sri Lanka said that it would test 15 of Google’s Loon balloons while countries like Indonesia and Australia are also experimenting with the technology.
The balloon floating over Yellowstone is likely part of a test that is taking place in Winnemucca, Nev., which is roughly 600 miles away from where the dirigible was spotted. Test balloons have also been spotted over Puerto Rico and Kansas.
In a recent navigation test, Project Loon balloons were deployed over Peru to test new artificial intelligence technologies that would keep the balloons in a specific region.
A spokesperson for Google declined to comment on the Yellowstone balloon.
It’s unclear whether the balloon was authorized to fly over the U.S. National Parks. Park regulations generally ban all types of aircrafts, which includes drones. However, balloons are not in the same category of aircraft as a drone.