Abstract Lake Balaton has the largest freshwater surface in Central Europe. The water budget of this shallow water body is characterised in most of the years with significant water excess, expressed in regular releases from the Lake through a partly artificial stream, Sio. Unexpectedly, negative annual values of natural water budget occurred in the period 2000–2003, virtually without any release from the lake following May 2000. This happened first time since 1921, i.e. the start of instrumentally measured water budget elements. The extreme situation has been manifested by quick drop of water levels. Water levels recovered during 2004, but the first release through control gates could be started only in September 2005. Components of the water budget are compared with the normal situation, and different exceedance probabilities, based on the previous 80 years. Besides the given analysis, an attempt is made to answer the question in the title by presenting a quantitative methodology and three parallel macro-circulation classifications. The lack of precipitation during the 4-year period could not be sufficiently explained by shifted frequency of the circulation types combined by conditional average precipitation. However anomalous behaviour of meso-scale processes strongly contributed to the given extreme situation, endangering not only tourism of the lake, but its flora and fauna.