Abstract
Zayandehroud is the water source for life in Central Iran, but it has become has turned into one of the most vulnerable ecosystem due to human disturbances. In this study, water quality and ecosystem health of Zayandehroud was evaluated in a segment of the river with permanent flow, from the Zayandehrud Regulating Dam to Pol-Kalleh. Water and benthic macroinvertebrate samples were collected from 11 stations during the summer of 2022. The Iranian Water Quality Index for Surface Water (IRWQISC), along with richness and diversity indices, as well as biological indices (BMWP and ASPT), were calculated. The findings revealed that the IRWQISC index categorizes water quality as moderate in most stations, with relatively good quality observed in only three stations. In contrast, the BMWP index denoted poor conditions, the ASPT index reflected severe to moderate pollution levels, and the Shannon diversity index also indicates severe to moderate pollution. The IRWQISC index was unable to accurately capture the effects of water flow interruption downstream of the Cham-Aseman diversion dam and its impact on the deterioration of water quality and overall river ecosystem health. However, the substantial decline in the richness index and biological indices at the Pol-Kalleh station highlights a significant ecological imbalance in the river ecosystem.