Thousands of naked bicyclists rode at night on Sunday in Portland near the city’s waterfront.

The World Naked Bike Ride promotes bicycle use for transportation.

“This is just a way of drawing attention to the need to be more green and replace fossil fuels with natural power,” said Ken Johnson, a naked rider, according to Reuters.

The event has also been celebrated in San Francisco, Seattle and Boulder and Black Rock City in Colorado since it began in 2004.

The city’s tolerant public indecency laws permit such activities.