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, will be determined, and amendments to the national water legislation will be proposed to mitigate the impact of regulation. During the field research, hydromorphological and fish data will be 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 will be applied to establish the E-flow. The TRANSWAT project will use the agreed methodology developed by the Interreg Latvia-Lithuania (ECOFLOW) project for modelling environmental flows. Ecological flow calculations will also be performed on an online modelling platform that will be developed as part of the recently launched LIFE GoodWater IP project. Based on the results of the assessment, the functioning of the HPP cascade will be 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 will be proposed to mitigate the consequences of river flow regulation.

The second part of the study is devoted to the assessment of the ecological status of five transboundary lakes 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 will be collected through water quality and quantity monitoring, as well as in-depth biological research. Combining new data with detailed analysis of lake basins (assessing the interaction of surface and groundwater and quantifying pollution sources using mathematical procedures) will determine the ecological status of the five lakes. A general methodology for assessing the well-being of lake ecosystems will be developed and tested at the pilot lake Garais/Ilge. To ensure the sustainability of the project results and further improvement of the ecological status, an agreed Latvian-Lithuanian Monitoring Program (MP) and a Program of Measures (PoM) will be developed.

During the implementation of the tasks envisaged in the first part of the research, information on the current ecological status of the Varduva River and indicators of the quality elements were collected, as well as information on the impact of various human economic activities on the ecological status of the river. Below each of the five hydropower plants installed on the Varduva River, representative sections of the river were selected and fish surveys were performed. Fish studies were performed in each of the hydromorphological units identified in the selected sections, which have specific characteristics of bottom substrate, depth, current velocity and shelters suitable for fish. Based on the research data, the distribution of fish species in various hydromorphological units was assessed, as well as the deviation of fish metrics from natural conditions in all surveyed sections of the river. The general patterns of changes in the status of the fish community in the gradient of HPP cascades have been established and the main drivers of change have been identified. The testing of conditional habitat suitability criteria for different fish species was completed. The criteria will be used for further modelling of the suitability of the habitat at different flows, using the MesoHABSIM model for this purpose, and for determining the optimal ecological flow.

In the course of fulfilling the tasks foreseen in the second part of the study, existing information on ecological status of five transboundary lakes was collected. Also, information was collected on the nature and intensity of human economic activity in the basins of these lakes and screening for potential sources of pollution was carried out. Automatic level gauges were installed on two lakes and removed after completion of measurements, which lasted from December 2020 till March 2022. Detailed data on water level changes is currently used in a comprehensive assessment of the ecological status of lakes. Fish community surveys were carried out in all five lakes. Data collected during fish research in the transboundary were analysed and the deviation of fish metrics from natural conditions was assessed. The ecological status of the lakes was determined based on the Lithuanian lake fish index. The deviation of fish metrics in lakes that do not meet the criteria for good status was assessed in the context of potential anthropogenic pressures. In parallel, a methodology for comparing systems for assessing the ecological status of lakes based on Latvian and Lithuanian fish indices is being tested.


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.

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