Changes of submerged vegetation over the last 50 years in lakes Dusia, Simnas, Žuvintas and Amalvas, related with re-arrangement of the Dovinė river basin and alteration of the hydrological regime are discussed. The study is based on reference information and data of recent field investigations.

Most significant changes of submerged vegetation were revealed in the shallow Lake Žuvintas. Twenty species of submerged plants became extinct (8 Charophyta, 10 Potamogeton, 2 Bryophyta) in the period from 1961 to 2004. The group of extinct plants includes sparse in the lake and rare in Lithuania species (Tolypella prolifera, Nitella syncarpa, N. mucronata, Fontinalis hypnoides). Formerly abundant and dominant species, such as Chara globularis, C. strigosa, C. hispida, Nitellopsis obtusa, significantly decreased. The increase of the number of charophytes and their abundance in 1997 has indicated that reduction of inflow of nutrients from the basin can significantly improve the state of submerged vegetation in the lake.

Significant changes took place only in the deepest (8–10 m) zone of the deep Lake Dusia (mean depth 15.7 m). Vegetation of this zone after damming did not recover and communities formed by filamentous algae and mosses became extinct. The zone of vegetation distribution reduced from 9 to 6 m depth limit.

It is possible that in the last 50 years charophytes became extinct in Lake Simnas, whereas in Lake Amalvas pondweeds and possibly charophytes disappeared.

Keywords: macrophytes, submerged plants, Charophyta, Potamogeton, lakes, Lithuania