Amsterdam city council has dropped its plan to let off 150,000 helium balloons to celebrate the investiture of king Willem-Alexander on April 30.

Mayor Eberhard van der Laan said on Monday the plan would be put on ice because of the fears many people have about the effect of the balloons on the natural environment.

The balloons would have been biodegradable but environmental groups said they would still pose a threat to animals and birds.