L. Forró szerk.: Miscellanea Zoologica Hungarica 8. 1993 (Budapest, 1993)

Vida, A.: Expected effects of the Gabčikovo river barrage system on the ichthyofauna of the Szigetköz and its values

MISCELLANEA ZOOLOGICA HUNGARICA To m us 8. 1993 p. 35-44 Expected effects of the Gabcikovo river barrage system on the ichthyofauna of the Szigetköz and its values by A. Vida (Received June 22, 1993) Abstract: On 25 October 1992, Slovakia diverted the main channel of the river Danube at Cunovo. As a result, the water types and as a consequence, their fishfauna of the Szigetköz located below this point were negatively affected, though to a different degree. Key words: Fishfaunal changes, hydropower dam, threatened fishes, Gabcikovo river barrage system, Szigetköz Introduction The Czechoslovakian and Hungarian governments agreed in 1977 to construct a 200 km long joint barrage system on the shared part of the river Danube. The new political system in Hungary suspended the Hungarian participation, while the (then) Czech and Slovak Republic decided to continue and eventually to complete the project. In turn, Hungarian scientists started multidisciplinary studies on the assessment of the possible environmental effects of the damming and other water regulations. The planned barrage system consists of three dams. The lowermost one at Nagymaros (40 km upstream of Budapest) was planned in a wholly Hungarian territory, and its construction was interrupted in 1989 in a still preparatory phase. The middle dam is located at Gabiikovo, Slovakia, and has recently been completed. The uppermost barrage serves as a river diverting system directing the river into the artificial channel leading to the hydroelectric power dam of Gabcikovo ( = Bős). Consequently, most of the original river flow is diminished causing drastic modification (degradation) of the landscape and its ecosystems, eliminating one of the very few surviving potamofaunal "paradises" of Europe. On 25 October 1992, the Slovakian party opened the artificial channel at Cunovo ( = Dunacsún), to start the operation of the hydroelectric power dam. With this unexpected measure, which was taken without considering ecological consequences, all the previous agreements were violated. As a result, downstream Cunovo, most of the water of the side-branch systems of the Danube in the so called "Szigetköz" (Hungary) and "Csallóköz" (Slovakia) areas disappeared within few hours. Approximately 70 percent of the side-branches located in the Szigetköz area became dry. Only a handful of patches of water remained in the once flooded areas, and these loose their respective surfaces continually, due to decreasing ground water levels. The unexpected inundation arriving at the end of November 1992 brought the water back to the flood-plain, but the process itself as described above, continues.