Waters in Belarus do not only benefit population and industries but can be a great troublemaker. First of all it concerns spring, and summer-autumn floods in the Pripyat and W. Bug basins. Flood damage is quite substantial. For example, losses caused by the summer flood of 1994 made up to US $100 mln. On top of that the sources of agricultural drinking water supply get polluted in flooded areas. For this reason predicting of disastrous water discharges as well as implementation of flood defense measures are of crucial importance.

A flood is a great overflow of water covering large areas and one of the natural disasters. High water, jams, inrushes, and breaks of dams can cause it. Spring floods are the result of snowy winters without thaws, rapid snow melting accompanied by abundant precipitation. Floods of such a type were recorded on the Neman in 1958 (the most significant for the last 150 years), on the Pripyat in 1970 and 1977, in the upper flow of the Dnieper and Western Dvina in 1908 and 1931. Summer-autumn floods are caused by intensive abundant precipitation. Large-scale floods were recorded in 1948, 1950, 1958, 1960, 1974; the 1974 autumn flood (it has been the most damaging for the last 120 years) involved the Western Bug and Pripyat basins; in October quantities of precipitation in some places were 3 to 6-fold above average. Winter take place floods more often in the Neman and Western Bug basins during intensive thaws. Flood defense action involves flow control.

High water is a relatively steady increase in water content, which repeats in the same season every year and is accompanied by a high and prolonged rise in water and overflow from the estuary onto its floodplain. In Belarus high water is the result of a snow blanket melting. It starts in the southwest in yearly March first, then begins in the north in the third decade of March. It finishes in the Neman basin in the late April - the beginning of May, in the W. Dvina and Pripyat basins it happens in late May - early June. The duration (30-120 days) depends on the amount of snow, depth of frost penetration, temperature, the length of a river, forest density, amount of lakes and other factors.

In the north and in the northeast the maximum levels of high water on medium rivers are 4 - 6,5 m and on small rivers 2,5 - 3,5 m, its rise continues 15-20 days and abatement - 36 - 40 days. In the west the maximum levels range from 2 to 3 m and 1,5-2 m respectively, its rise continues 8-12 days and abatement - 25-30 days. In the south-west and south the high water period is extended and smoothed. Its duration is 60 – 80 days with exceeding of minimum summer levels by 1,5-3 m. In the south high water continues for 25 - 30 days on the floodplains of small rivers, and 45-60 days on medium and large rivers, with a dominant width of 1,5-2 km and a depth of 0,3-0,8 m on the floodplain. In the Neman, Sozh and Berezina basins the duration of high water is 8-12 days, the width of overflow on small and medium tributaries varies 0,3 - 0,5 km, on large ones 2-3 km; the floodplains are flooded 0,5-1m in depth. The floodplains of rivers in the W. Dvina basin are more rarely flooded, the depth of overflow there is 1-1,5 m. The high water period on lakes is 2- 3 times as long as that on the neighboring rivers, the difference in levels is 2-3 times less. The average level of high waters is 43 - 167 mm. The decrease in a spring flow from north to south and from northeast to southwest has been observed. 36 - 77 % of the annual flow of the Belarusian rivers fall on the high water period.

In this period the high water causes damage to facilities and bank erosion, as well as covers valuable agricultural lands with sand. In Belarus the maximum of high water was recorded on all the rivers in 1931, 1956 and 1958, in the Neman and Dnieper basins in 1947 and 1970, in the Pripyat river in 1979. In order to avoid overflowing the reinforcement works are performed on river banking; polders, dams and reservoirs are built. Record on spring high water is needed for designing and maintaining bridges, dams and other national entities in river valleys, for operating reservoirs and water use.

High water in contrast to floods is relatively short-term and non-cyclic sharp rises in water levels and an increase in river flow after heavy rains and long thaws. They have their maximum height and duration in late summer and in the period of autumn drawn-out rains. A summer rise in water reaches 3-3,5 m on small rivers northwest, 1 m south, 1,5-2,5 m on the rest of the territory. The duration of summer-autumn high water is 20-30 days, on most of territories it takes place once or twice in summer and autumn. The peak of high water due to heavy rains was recorded in 1962; the most disastrous flood (such a flood happens only once in a hundred years) occurred in the autumn of 1974 and covered the Western Bug and Pripyat rivers. Winter floods more often occur in the west and southwest (1-2 times per season). Intensive high waters cause floods, less significant ones wash away hay from meadows and destroy crops on floodplains.