YELLOWSTONE NATIONAL PARK, Wyo. (AP) — Rangers have not been able to spot the unmanned drone that crashed and sank in a hot spring at Yellowstone National Park last weekend.

Park spokesman Al Nash says rangers are considering using a helicopter to see if they can spot it from the air.

Even if they find it, Nash says that it's not known if the drone can be removed from the Grand Prismatic Spring.

The Grand Prismatic is the third-largest hot spring in the world and is up to 160 feet deep. It's best known for vivid colors.

A drone expert says he has concerns drone materials could harm the hot spring.

Nash says no decision has been made on citing the drone operator, who notified authorities of the incident.