The aim of this study was to assess the potential impact of trout farm effluents on water quality of Karasu stream (Bozüyük-Turkey) where a ring of five trout farms are localized and to estimate the phosphorus load of the farms. Monthly samples were taken from upstream (1. station) and the last trout farm effluents (downstream- 2. station) for 11 months. Trout farms had a significant impact on dissolved oxygen (DO), biological oxygen demand $(BOD_5), NO_2-N, NO_3-N$ and total phosphorus (TP) concentrations of Karasu stream (P<0.05). Changes in pH, total suspended solids (TSS) and ammonia-nitrogen $(NH_3-N)$ concentrations were insignificant (P>0.05). During the study period, measured values of the last trout farm effluents were within the effluent limits for trout farming in different countries. The total annual phosphorus load of trout farms on Karasu stream was estimated as 12,205 kg. On average production of 1 ton of trout production resulted in load of 9.38 kg of phosphorus. The average phosphorus load of 1 ton of feed used was estimated as 8.09 kg.
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