Are fountains islands in the "urban sea"? We studied chiromonid assemblages of twelve fountains located in Olomouc (Czech Republic) and in Copenhagen (Denmark). In total, 45 taxa dwelled the fountains, varying from 4 to 23 in particular sites. The typical fountain community seems to be a unique assemblage, constituted of species linked with tap-water, hygropetric and semi-terrestrial habitats as well as more common species with very wide geographical distribution and ecological requirements. The fountains surveyed demonstrate some basic aspects of the island biogeography. Even though there was no linkage between taxa richness and fountain area or distance from the colonization source, a strong correlation between similarity of chironomid assemblage structures and distance to river source (Olomouc), and geographical proximity (Copenhagen) was recognized. Generally, distance to natural aquatic sources, fountain proximity and regional factors determine the chironomid composition of fountains.