A windmill is seen in the Keukenhof garden in Lisse, Netherlands April 19, 2019. As spring flower fields around the Netherlands burst into bloom, painting the countryside with dazzling swathes of red, white, and blue, a modern day tulip bubble may be forming: tourists. REUTERS/Yves Herman

Tourists pose in front of tulips at the Keukenhof garden in Lisse, Netherlands April 19, 2019. More than a million foreign sightseers are expected to visit this country of 17 million people on Easter weekend, a record, the Dutch Tourism Bureau said. REUTERS/Yves Herman

An aerial view of tulip fields near the city of Creil, Netherlands April 18, 2019. REUTERS/Yves Herman

An aerial view of tulip fields near the city of Creil, Netherlands April 18, 2019. REUTERS/Yves Herman

An aerial view of tulip fields near the city of Creil, Netherlands April 18, 2019. REUTERS/Yves Herman

An aerial view of tulip fields near the city of Creil, Netherlands April 18, 2019. REUTERS/Yves Herman