Preparing three strategic barrier removals in the Ljubljanica catchment, Slovenia

Introduction

The project area is located within the Ljubljanica River catchment and the wider protected landscape surrounding Lake Cerknica, one of Europe’s best-known intermittent karst lakes. The area forms part of an ecologically important network of wetlands, floodplains, sinking rivers, springs and underground watercourses, much of which is designated under Natura 2000 and the Ramsar Convention.

The project focuses on three connected rivers: the Stržen, Cerkniščica and Rak. These rivers are part of a complex karst hydrological system in which water flows both on the surface and underground.

The three rivers support valuable freshwater habitats and native fish populations, particularly the brown trout (Salmo trutta fario) and European bullhead (Cottus gobio). However, their ecological continuity is disrupted by three obsolete barriers at Narte, Dolenja Vas and Rakov Škocjan. These structures obstruct fish movement, interrupt natural sediment transport and reduce connectivity between spawning, feeding and refuge habitats.

Project context and opportunity

The Stržen, Cerkniščica and Rak rivers form a connected system of surface and underground flows that supports Natura 2000 and Ramsar habitats, as well as valuable native fish populations, including brown trout and European bullhead.

Despite the area’s high conservation value, river continuity is disrupted by three obsolete barriers at Narte, Dolenja Vas and Rakov Škocjan. These structures no longer serve an essential function but continue to obstruct fish migration, interrupt sediment transport and fragment spawning, feeding and refuge habitats. The main opportunity is therefore to prepare all three barriers for future removal by completing the required technical surveys, engineering designs, environmental assessments, legal clarification and permitting documentation.

Once removed, the barriers are expected to restore connectivity across approximately 36 km of upstream river habitat, improve ecological processes and strengthen the resilience of one of Slovenia’s most important karst freshwater systems.

Project aims

The project team’s overall goal is to prepare three obsolete barriers, at Narte, Dolenja Vas and Rakov Škocjan, for future removal by completing all technical, environmental, legal and permitting work required for implementation.

The specific goals are to:

• carry out detailed topographic, hydraulic and site surveys for each barrier;
• prepare barrier-specific engineering designs, demolition methods, sediment-management measures and cost estimates;
• assess ecological impacts and define mitigation measures to protect native fish and sensitive habitats;
• clarify ownership, legal status and permitting requirements;
• agree appropriate solutions for local access, especially at Dolenja Vas;
• produce complete demolition-ready documentation and an implementation roadmap for the next project phase.

The expected outcomes are:

• three barriers fully prepared for removal;
• confirmed technical and legal pathways for implementation;
• improved readiness for a future Open Rivers Programme removal grant;
• restoration of approximately 36 km of upstream river connectivity once the barriers are removed;
• improved fish migration, sediment transport and habitat continuity;
• better conditions for focal species, particularly brown trout and European bullhead;
• stronger ecological resilience of the Stržen, Cerkniščica and Rak river system and the wider Lake Cerknica karst landscape.