The water balance of the Neusiedler See and its surroundings is almost exclusively determined by evaporation and precipitation. There are no bigger rivers that could flow into the Neusiedler See. The changing water levels determined the life of the Seewinkel population. Drainage systems of the last 150 years have influenced the water levels of the region.
The catchment area, about 1.120 km² big, is quite small compared to the size of the lake. The largest part - more than 80% - of the water balance of this 320km² lake comes from precipitation. This has often caused extreme fluctuations of the water level and even complete desiccation.
For the past 100 years, the lake has been regulated by the Main Regulation Channel; that is to prevent flooding. The Main channel is therefore used as an instrument to reduce high water levels. Extremely high water levels can be prevented this way. The Austro-Hungarian committee for water bodies, composed of experts in hydraulic engineering, supervise the water gate together. The lock chamber is accessible to everyone: it is located on the street from Sarród (near Fertöd) to the direction of Fertöújlak.
It is especially during extreme dry or wet periods when the dependence of the water level on precipitation becomes obvious. The water levels can vary up to 60cm within one year. If precipitation in winter can compensate the evaporation of the last summer, the next rainy season during spring can cause high water levels and even flooding. On the other hand, if winter precipitation is poor, the water level of the Neusiedler See already drops in springtime.
Thunderstorms in midsummer can slow down the drop in the water level but cannot undo the effects of evaporation. The evaporation at this time of year, caused by wind and sunshine, is too strong. The water level of the lake is reaching a low level after two or three dry winters. Many dry winters in a row can cause desiccation of parts of the lake. From 1865 to 1871 was the last complete desiccation of the Neusiedler See. Analyses imply that the lake has desiccated about one hundred times to date.
Between 1990 and the summer of 1991 a definite decline in the water level could be observed. It then rose steadily, reaching the maximum of 115.96 m in spring 1996.
After 1996, the annual precipitation was clearly below the average. In 2003, the water level was at 115.08 m in autumn. Since 2006, the water level has increased up to 115.69m.
The groundwater of the Seewinkel is in no way connected to the Neusiedler See.
The fluctuation of the water level is even more visible when it comes to the saline lakes ("Lacken"). Many of the 40 saline lakes dry out every summer. Already in early summer, there is a white shimmer on some of the saline lakes. This is due to the salt that has climbed up to the surface from the near-surface stratum and crystallized out there.
This is the time when the heaviest evaporation takes place: sun, heat and wind minimize the surface of the shallow saline lakes rapidly. In dry years, the first saline lakes are dried out already in May. It is especially on days with strong winds, that the saline lakes dry out even faster, as the winds blow the shallow water onto the shore, which has already dried out.
The total desiccation does no harm to the saline lakes. Quite the contrary! If the groundwater touches the impermeable bottom of the Lacke from below, new salt can rise through capillary action.
Hollows and basins, that can be smaller than one square metre or larger than several hectares, fill with water from precipitation during wintertime. This water can not seep away because of the impermeable soil.
Thanks to these uncountable water bodies on the meadows and the pasture land, the Seewinkel is one of the most important wetlands in Central Europe. These water bodies - and their rich diversity - can be experienced until the late spring.
Human interference has changed the water balance of the area over the years. Drainage systems, like channels, direct the water to the Main Regulation Channel and finally into the Danube. This caused a drop of the ground water level in some areas. Nowadays, the Neusiedler See-Seewinkel National Park tries to provide water to formerly drained areas by means of specific water retention measures.