Effluent characteristics of flow-through trout farms and their effects on stream water and sediment quality

Over the past decade, the rapid expansion of freshwater aquaculture has raised concerns regarding its potential impacts on water and sediment quality in receiving streams. This study investigated the effluent characteristics of two flow-through rainbow trout farms and evaluated their effects on the water and sediment quality of the adjacent stream. Between March and August 2025, water samples were collected monthly from the inlet and outlet of both farms, while additional water and sediment samples were obtained at two locations along the stream-one upstream and one downstream. The results showed significant increases in total suspended solids (TSS), NH₄-N, and total phosphorus (TP) levels from the inlet to the outlet waters, whereas dissolved oxygen (DO) levels decreased significantly, likely due to the absence of effluent treatment processes at the farms. Major ion and metal concentrations showed only minor increases from the inlet to the outlet, indicating that farm activities had limited influence on these parameters. Predicted TN (total nitrogen) and TP fluxes obtained using the nutritional model were comparable to those estimated by the hydrological method. Significantly higher values of EC, COD, TSS, NH₄-N, TP, and sediment organic matter (OM) were recorded at the downstream station compared to the upstream station. Based on the DO, TN, TP and NH₄-N concentrations, the downstream station was classified as Class II water quality, indicating lightly contaminated water. Based on these findings, several management recommendations were proposed to safeguard the water quality of the receiving stream.