One of the most noticeable problems associated with water pollution is the bad smell of polluted water , an odour problem occurring when hydrogen sulphide gas is released from sediment that is rich in organic matter and low in oxygen 政府多年来一直致力解决避风塘水质污染问题，其中较易为市民察觉的一项就是臭味问题。臭味的成因是海床沉积物中的有机物质过高和含氧量低，因而形成硫化氢这类难闻的气体。
They are sulphide and free hydrogen sulphide . from 1989 , selected monitoring stations also monitored e . coli and faecal coliforms , which indicate faecal contamination from domestic sewage and animal waste . these two bacterial parameters were extended to all stations from 1999 自1989年开始，部分河溪监测站开始监测大肠杆菌及粪大肠菌群以显示住宅污水及动物粪便所造成的水污染其后在1999年起，所有监测站均测试此两项细菌参数。
In 2005 , 61 physical and chemical parameters were measured and analysed in sediments . these included particle size , electrochemical potential as highly anoxic sediment with negative potential is related to organic pollution , chemical oxygen demand which indicates organic pollutants , total sulphide inorganic constituents , source of the unpleasant - smelling gas hydrogen sulphide , 15 metals and metalloids aluminium , arsenic , barium , boron , cadmium , chromium , copper , iron , lead , manganese , mercury , nickel , silver , vanadium and zinc , and trace toxic organics pahs and pcbs - 16 compounds and 18 congeners respectively 2005年，沉积物监测包括分析61种物理及化学参数，其中有粒子大小电化学势有机污染促使沉积物缺氧，而让电化学势呈负数值化学需氧量显示有机污染程度总硫化物无机物，是造成难闻气体硫化氢的主因15种金属及准金属铝砷钡硼镉铬铜铁铅锰汞镍银钒及锌和痕量毒性有机物多环芳烃及多氯联苯分别为16种复合物及18种同质物。
The epd s long - term monitoring data indicates that the electrochemical potential of the sediment at sam ka tsuen typhoon shelter which reflects its oxygen content was substantially raised became less negative as a result of the bio - remediation programme , and the total sulphide level hydrogen sulphide gas , the source of the bad odour was significantly reduced 环保署的长期监测数据显示，三家村避风塘的沉积物经生化处理后，其电化学势反映水含氧量大幅提高负数值降低，而总硫化物水平导致臭味的硫化氢气体来源则明显下降。
