Except the dissolved oxygen (DO), all measured parameters between the two sampling sites fell into comparable ranges. The possible reason would be there is strong natural flow and most water movement is tidal. Due to this large movement, the channel is a good settlement basin for the pollutants either brought from upstream or by the flood tides. In addition, the minimal water exchange process also increases the self-cleaning power of the channel. The water qualities of two sites were similar due to the prohibition of pollutants loaded into the habitat set by Hong Kong law. Besides, algal blooms, sewage effluents and all fish feed and fish wastes disposed directly are three major environmental impacts resulting from low DO found in mariculture farm.