Joint management of Latvian – Lithuanian transboundary river and lake water bodies (TRANSWAT)

Projects leader: dr. Tomas Virbickas



The aim of the „TRANSWAT“ project is to ensure the joint assessment and management of transboundary river and lake water bodies whose hydromorphological and / or ecological quality may not comply with the requirements of the EU Water Framework Directive (WFD).


There are three Latvian-Lithuanian transboundary river basins in the Program area (Venta, Lielupe and part of the Daugava), where many rivers and lakes do not meet the criteria for good ecological status. Some rivers are classified as heavily modified water bodies due to changed hydromorphology, since their hydrological regime is regulated by cascades of hydroelectric power plants (HPP). Some of the transboundary lakes were previously delineated as water bodies only in Latvia. Therefore, monitoring of the quality of elements and assessment of anthropogenic impact on these lakes previously was carried out only in Latvia.


The project consists of two parts: (1) assessment and management of rivers regulated by HPP cascades, and (2) assessment and management of the ecological status of transboundary lakes.


In the first part of the study, the ecological flow (E-flow) of the transboundary rivers, which are regulated by the HPP cascades, was determined, and amendments to the national water legislation were proposed to mitigate the impact of regulation. During the field research, hydromorphological and fish data were collected to model the ecological flow (E-flow) in Lithuania (Varduva River with 5 HPPs) and Latvia (Losis River with 2 HPPs and Ciecere River with 3 HPPs). The MesoHABSIM model was applied to establish the E-flow. The TRANSWAT project used the agreed methodology developed by the Interreg Latvia-Lithuania (ECOFLOW) project for modelling environmental flows. Ecological flow calculations were performed on an online modelling platform that was developed as part of the recently launched LIFE GoodWater IP project. Based on the results of the assessment, the functioning of the HPP cascade was modelled using the HEC-RAS model (computer program for hydraulic modelling of water bodies) to ensure the ecological flow under each HPP and sustainable management of water bodies. Based on the obtained results and recommendations, amendments to the national water legislation were proposed to mitigate the consequences of river flow regulation.


Implementing the objectives of the second part of the study, the ecological status of five transboundary lakes was assessed in the basins of the Lielupe (Garais/Ilge) and Daugava (Galinu/Šalna, Kumpinišku/Kampiniškes, Lauceses/Laukesas and Skirnas). Three lakes (Galinu/Šalna, Kumpinišku/Kampiniskes and Lauceses/Laukesas) belong to the NATURA 2000 network. New data was collected through water quality and quantity monitoring, as well as in-depth biological research. Combining the new data with a detailed analysis of the lake basins (assessing the interaction between surface water and groundwater and quantifying pollution sources using mathematical procedures), the ecological status of the five lakes was determined. A general methodology for assessing the well-being of lake ecosystems was developed and tested at the pilot lake Garais/Ilge. In order to ensure the sustainability of the project results and further improvement of water quality, proposals for harmonisation of the Latvian-Lithuanian Monitoring Programme (MP) and the Programme of Measures (PoM) were developed.


Project implementation period: 01/10/2020 - 09/30/2022

Project number: LLI-533

Project acronym: TRANSWAT

Project budget: 607 466.51 EUR (partially funded by the European Regional Development Fund (ERDF) (516 346.53 EUR))

The project is funded by the Latvian-Lithuanian Cross-Border Cooperation Program 2014–2020.

Official website of the EU: