Summary:

The article contains results of an investigation on contents of oxygen de-mand in fish ponds water fertilized with biologically treated municipal sewage. Additionally, during collection of water samples there were also analyzed water reaction and pond’s water temperature. Researches were carry on in vegetative season in 2006. The object of research was fish pods of Komorowice complex, which are located in North part of Bielsko-Biała. The chosen ponds: Green and Stone are characterized with individual inflow and outflow of water. The chose ponds are characterized with different technical parameters. Green pond is shallow one – its average depth is about 1 m, with area of 4,2 ha, which give water capacity of pond 42 000 m3. In turn Stone pond have smaller area – 3,3 ha, but is almost two times deeper then Green; its average depth is about 1,7 m which also give greater water capacity of pond: 59 200 m³. In paper were qualified changes of oxygen demand, temperature and water reaction in pond’s water. Additionally, were qualified basic statistical parameters of analyzed indi-cators: an average, minimum, maximum value, standard deviation and interval. Analyses made in ponds showed, that in 2006 vegetative season contents of oxygen demand in Green pond included itself between 2,0–7,4 mgO₂∙dm^-3, in-stead in Kamienny pond between 2,2–11,47 mgO₂∙dm^-3. Lower contents of oxygen demand in periods with intensive growth of duck weed were observed. In turn, in periods with lower amount of duck weed increase of content of oxygen demand were observed. In both ponds, from the end of July seasonal variations were ob-served. In this period mortality of fish increase were also observed what was connected with developing of illness of carp (Koi Herpes Virus) on the oświęcim valley. Water reaction was nearing in both ponds. Into the half of the season a lit-tle bit higher value of reaction in Green pond were observed. Instead in the end of the season there were convert situation: higher values were in Stone pond. Also thermal conditions in both ponds were similar in whole analyzed season. From the beginning of June to the end of August water temperatures in analyzed ponds crossed 20ºC and were connected with high temperature of air observed in this period.