Study of river segments

In the international Venta river basin district, experts surveyed segments of the Ciecere river in Latvia, where the Ciecere, Dzirnavnieki, and Pakuļi HPPs operate, segments of the Losis river, home to the Grantiņi and Lejenieki HPPs, and segments of the Varduva river in Lithuania, where the Kulšėnai, Renavas, Vadagiai, Ukrinai, and Juodeikiai HPPs are located.

Each river segment downstream of the hydroelectric power plants (HPPs) was surveyed four times under varying hydrological conditions. During each site visit, the areas occupied by different river habitats were measured and mapped in detail, along with river depth, flow velocity at several points within each habitat, riverbed type, and other indicators.

Sharp fluctuations in river water levels were observed over very short periods, causing the washing away of aquatic animals and the destruction or significant degradation of suitable fish habitats. In cases where insufficient water levels are maintained downstream of an HPP, aquatic organisms incapable of rapid movement (e.g., molluscs) can suffer mass mortality in that river section. Furthermore, in the case of HPP cascades, the operational regime of downstream HPPs is also dependent on the activities of those located upstream.

The analysis of the obtained data and the results of river habitat modelling led to the conclusion that the currently permitted minimum guaranteed flow and ecological flow required from small-scale HPPs by legislation are significantly lower than the flow actually necessary to support the life processes of aquatic organisms.

Ecological status of transboundary lakes

Data obtained by experts on the ecological status of the lakes allowed for the development of a unified Latvia–Lithuania monitoring programme for five transboundary lakes (Ilzu (Garais) in Zemgale, and the Lielais Kumpinišķu, Galiņu, Laucesa, and Skirna lakes in Latgale).

An assessment of anthropogenic pressures on these lakes indicates that the most significant factor is pollution in bottom sediments, which has accumulated over the past 50–70 years. In developing the Latvia–Lithuania programme of measures for improving the ecological status of these lakes, experts concluded that detailed additional research is required into practically feasible water body remediation methods. (...)