The protesters, backed by the Association of Fishermen at the Chamber of Crafts in Rijeka, consider the location of the former company "Torpedo" to be unsuitable for a new fishing harbour, arguing that it would not be possible for fishing boats to enter or leave harbour safely, particularly in bad weather.
The fishermen said that they had sent their objections to the city authorities, but that they had not been taken into consideration.
They believe that the new harbour will not ensure normal working conditions for about 150 fishermen in Rijeka.
The relocation of the harbour is planned under the World Bank-funded Rijeka Gateway Project, which provides for the modernisation and reconstruction of the Rijeka harbour and access roads by 2010.