A feasibility study on using the long?term datasets to clarify the main factors influencing the ecological status in the Thames Tideway was carried out. The datasets between 1915 and 2006 show the clear phases of deterioration, recovery and stable improvement. The period of 1940s to 1960s saw the worst conditions in the tideway with relatively high temperature, NH_4? N and BOD_5 as well as low dissolved oxygen. Few invertebrates were recorded during that period. Since 1960s, there has been a general trend of recovery in terms of water quality and invertebrate community. Generally, fluctuations in the numbers of invertebrate species were linked more to the changes in the water chemistry, especially dissolved oxygen than in the water temperature. Although there were many large gaps in the data of invertebrates and water chemistry especially before 1960 in Thames Tideway, it is still necessary to examine all the datasets more thoroughly to establish the quantitative relationships between water variables and invertebrate community in future studies. A feasibility study on using the long? Term datasets to clarify the main factors influencing the ecological status in the Thames Tideway was carried out. The datasets between 1915 and 2006 show the clear phases of deterioration, recovery and stable improvement. The period of 1940s to 1960s saw the worst conditions in the tideway with relatively high temperature, NH4N and BOD5 as well as low dissolved oxygen. Since 1960s, there has been a general trend of recovery in terms of water quality and Generally, fluctuations in the numbers of invertebrate species were linked more to the changes in the water chemistry, particularly dissolved oxygen than in the water temperature. Although there are many large gaps in the data of invertebrates and water chemistry especially before 1960 in Thames Tideway, it is still necessary to examine all the datasets more thoroughly to establish the quantitative relationships between water variables and invertebrate community in future studies.