Altered hydrological connectivity between lakes and rivers may impose significant effect on lake ecosystems.Due to lacking of long-term data on lake environmental changes,the process and mechanism of limnological response to the changes in hydrological connectivity is still unknown.This work chose Lake Zhangdu from the Yangtze floodplain,to investigate the long-term (about 200 years) environmental changes responding to altered connectivity with Yangtze River using a high-resolution multi-proxy analyse on 210 Pb/¹³⁷Cs dating,diatom,geochemistry and grain size.Palaeolimnological records revealed that the lake has experienced three changes of the hydrological connectivity with Yangtze River,which matches well with the documentary records.Prior to 1954(stage I),the lake connected naturally with the Yangtze River and a low-nutrient,relatively deep and disturbed lake condition was inferred based on the high abundance Cyclotella bodanica.After 1954,with a dam construction(stage II),water residence time of the lake became longer and hence decreased in clarity,which favors the growth of Aulacoseria granulata.Correspondingly, nutrient enriched gradually which indicated by the slightly increase of eutrophic diatoms,as well as significant higher concentration of TOC and sedimentary TP,TN.In recent 20 years,lake became more eutrophicated inferred from high percentages of eutrophic species C.meneghinena,A.alpigena,Nitzschia palea,Surirella minuta and geochemical records including TOC,sedimentary TP,TN.After 2005(stage III),the lake condition improved slightly,indicated by diatom assemblage change with the increase of benthic species,although the concentration of TOC and sedimentary TP,TN were still high.Consequently,reconnection with Yangtze River may be an effective manner to relief the stressed floodplain lakes.