A ban on smoking marijuana on the streets of Amsterdam's red light district went into effect on Thursday, part of a push by the city's first female mayor to clean up the area.
Signs were posted in the canal-lined neighbourhood known for its brothels, sex clubs and marijuana cafes, which attract millions of tourists a year, but are a nuisance to residents.
People caught violating the ban now risk a $110 fine.
City mayor Femke Halsema has promised to improve conditions for sex workers and reduce crime and excessive use of drugs and alcohol.
Discussions are underway to move sex and drug tourism out of the city centre, but there is opposition from residents in locations that have been proposed as alternatives.
People will still be allowed to smoke inside and on the terraces of coffee shops selling marijuana and hash in the district and other parts of the city.
The personal use of small quantities of marijuana is tolerated by authorities in the Netherlands.