Summary:

Small water reservoirs are principal elements of small retention. Reservoir built in Zarzeczany village (Gródek commune, Podlasie region) in 2000 is the example of such object. It is localized in wide, wet, and flat valley. Water to the reservoir is supplied by melioration ditch receiving waters from catchment runoff and, during summer droughts, from river Gleniówka. An apparent effect of surface runoff on water quality was observed in the reservoir. It was found that after the rainfall, values of many tested water parameters (color, turbidity, phosphates, COD-Mn, ammonia, nitrates) were increased. The concentration increase of indices responsible for water contamination with organic compounds at simultaneous relatively high color indicated the humus origin of that contamination.