(BOULDER CITY, NV) —  Tourists visiting the Hoover Dam Tuesday morning in Nevada witnesses an explosion and a plume of black smoke, so they whipped out their cell phones and started recording.

Apparently, a blown transformer is blamed for causing the explosion at the Hoover Dam.

One woman can be heard on cell phone recording saying, “My goodness, something has blown up!”

Witnesses first saw black smoke billowing up from the side of the dam around 10:00 a.m. Tuesday morning.

Tours of the dam were halted for about 30 minutes while Nevada firefighters put out the blaze.

The Bureau of Reclamation released a statement saying a transformer in the Hoover Dam caught fire but there is no risk to the power grid and no one was injured.

Officials are still investigating the cause of the fire but the dam has re-opened to the public.