The freshwater ecosystem has mostly been susceptible to human interventions due to the exploitation
of hydropower in the last century. The consequences of these interventions are increased numbers of
endangered fish species and species categorized by the International Union for Conservation of Nature
(IUCN) Red List as likely to become extinct or even extinct species. Ensuring the smooth transfer of
watercourse is essential for fish to pass, for conservation of endangered as well as other fish
populations. Fish need various habitats for living; for example, for spawning, growing, nourishment,
movement. Where there is an impassable obstacle in the watercourse, there should be an organised
natural or a technically built fish ladder. On the way to the Sava River estuary, there are a few
impassable obstacles in the Ljubljanica River and because of that; the quality of habitats has changed
fundamentally for fish and other water organisms. As a part of the project “Ljubljanica Connects –
The Restoration of the Corridor of the Ljubljanica River and the Improvement of the River Regime”,
the fish ladder next to the Plečnik sluice at Ambroţ square has been restored. The purpose of the
project is to improve and connect the habitats of the endangered species in the Ljubljanica River; such
as Danube Salmon (Hucho hucho), Danube Roach (Rutilus pigus), Striped Chub (Leuciscus souffia);
that is species, protected by regulations. The thesis presents the problem of the migration of fish, or
non-functionality of fish ladders before the renewal. Fish had not been able detect the passage. I
summed up the renovation measures and the improvements in the fish ladder as well as established the
functionality of the ladder with measuring the flow and the speed of the water flow at the entrance as
well as in the middle of the fish ladder. The purpose of the project “Ljubljanica Connects” is also to
raise awareness among people that the establishment of the smooth transfer of watercourse is essential
for fish populations. It is vital we do this out of respect for nature and legislation that dictates the
renewal of all the existing fish fishways and the construction of new areas where people will interfere
with watercourses.
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