Culvert mapping and removal prioritisation in Gauja River catchment

Addressing the often-overlooked impact of road crossing barriers on critical headwater river ecosystems by using GIS mapping and developing a methodology to prioritise them.


The Gauja River Basin covers 15% of Latvia’s territory, and around 10% of Latvia’s population lives there. The river flows through relatively scarcely populated parts of Estonia and Latvia. The Gauja River Basin is naturally affected by the climatic conditions of the very variable terrain. The Gauja National Park protects 90,000 hectares of the basin, and forests cover 52% of the area. Thus, the river basin is less affected by pressures from the agriculture sector, and the potential removal of culverts will be easier, as several of them will be located in the national park, which is a protected area. The basin is an important habitat for endangered salmonid and lamprey species. It is relatively open to fish migration as no major dams have been constructed in the lower to mid reaches of the river.

At a glance

Project typeIdentification and prioritisation
Project statusLive
Focal speciessalmonoid and lamprey
Project website

Project context and opportunity

The Gauja River Basin is an important habitat for various endangered salmonid and lamprey species. However, many potential spawning habitats in the upper reaches of the Gauja tributaries are currently blocked for migration due to unpassable culverts, and their locations are largely unknown. By visiting, mapping, and prioritising these small barriers, the project team will have taken an essential first step towards restoring the river and its biodiversity. By creating this list of priority road dams in the Gauja River Basin, there will be a clear roadmap to refer to in the future when planning river connectivity and restoration activities. Additionally, the team will develop a methodology for mapping problematic culverts in a river basin and be able to share lessons learnt for the mapping of the other river basins in Latvia and Europe.

Project aims

The project aims to develop a way to easily identify impassable culverts that can be removed to open up small rivers and tributaries. Using GIS mapping, the team will, for the first time, map an entire river basin in Latvia, identify 100 of the most likely barrier sites, visit them in person, and confirm whether the GIS mapping has been accurate in deeming these sites as barriers. They will then develop a methodology that can be used in other Latvia basins and beyond to easily identify problematic culverts. The ultimate goal is to identify easy-to-remove barriers so that more rivers can be made free-flowing.


The “Mapping of Impassable Culverts in the Ecologically High Priority Gauja River Basin” project has made significant strides in understanding and addressing barriers to fish migration in the Gauja River Basin. Spanning from August 1, 2023, to February 29, 2024, the project, led by Pasaules Dabas Fonds in association with WWF, alongside project partners Jāņa Sēta, SIA Saldūdeņu Risinājumi, and the Scientific Institute of Food Safety, Animal Health, and Environment “BIOR,” aimed to identify and prioritise culverts hindering fish migration within the basin.

Through remote mapping using GIS technology, field visits to assess culvert accuracy, and prioritisation based on a model developed by BIOR, the project has shed light on 98 identified culverts, of which 74% were found to be problematic or impassable. The project team have created a list of 20 culverts as significant barriers to fish migration and are prioritising them for removal. This strategic removal of culverts underscores the project’s commitment to tangible river restoration outcomes and contributes to the overarching objectives of ecosystem preservation.

The project’s findings provide valuable insights into the Gauja River Basin’s ecological challenges and lay the groundwork for future conservation efforts. By identifying and prioritising culverts for potential removal or mitigation, the project contributes to the broader goals of restoring river ecosystems and safeguarding aquatic biodiversity. Moving forward, continued collaboration and targeted action will be essential in addressing the complex issue of barriers to fish migration and promoting the health and resilience of the Gauja River Basin.

Read their progress report.