Three and six metres high, the sculptures represent whales emerging from a sea filled with plastic waste. They were made by Italian Greenpeace activists.
The sculptures are covered in plastic bags from shopping malls, which underlines the problem of the lack of responsibility in the management of plastic waste in Croatia.
Greenpeace campaign director Petra Andric said the campaign was closely related to the adoption of a European directive on disposable plastic bags and was aimed at prompting the Environment and Energy Ministry to see to it that the directive was implemented as soon as possible.
The activists called on citizens to sign their petition in Zagreb's main Ban Josip Jelacic Square or on Greenpeace's website (Greenpeace.hr).