Natural flow plays a vital role in forming biotic diversity by controlling essential environmental conditions within the river channel and floodplain. This paper assesses the changes in streamflow and ecology caused on Krishna River by Srisailam dam. Regulated and unregulated river flow discharge data were collected at Nagarjuna Sagar gauge station which is located downstream of Srisailam dam. Flow Health (FH) software developed by the International Water Centre, Brisbane is used to calculate the hydrological alteration and environmental flow requirements due to Srisailam dam. Results show that impoundment of the dam mainly decreases the high flows by storing flood flow for water supply, irrigation purposes, etc., and enhances low flows due to hydropower operation. Regulation of the dam significantly affected the mean flow in August, September, and October. Mean annual flow (MAF) decreased considerably and seasonal flow shifted. The minimum flow released from the dam to downstream was calculated by two options, namely, low risk and medium risk to the environment. Low risk achieved a score of 0.61 FH and 0.5 FH was achieved by high risk, with a MAF volume of 40% (i.e., 7,225 m3) and 30% (5,847 m3), respectively.