Comparisons of Water Quality near Cage Culture Sites in Batang Ai Reservoir, Sarawak, Malaysia

New development and expansion of cage culture at Batang Ai Reservoir would require investigation of the water quality. Therefore, the objective of this study was to determine the water quality at three existing aquaculture sites, one abandoned site, and one station without cage culture at three different depths. This study was carried out in October 2013 during the rainy season. Water quality was measured in-situ and water samples were collected and analyzed according to standard methods. Results showed that dissolved oxygen concentrations at the surface is sufficient for healthy aquatic organisms. However, dissolved oxygen at 10 m is not suitable for healthy aquatic organisms. All aquaculture sites showed significantly higher conductivity and ammonia-nitrogen at 20 m depth than the station without aquaculture. The aquaculture site that has been abandoned for nine months still showed higher 20 m chlorophyll-a and surface phosphate. Elevated surface, biochemical oxygen demand, phosphate and nitrate were observed at the largest and oldest aquaculture site. Based on the Chl-a concentration, the stations are classified as mesotrophic. This study showed that cage culture activities at Batang Ai Reservoir has impacted the water quality. Hence, further monitoring of water quality in the reservoir needs to be carried out.