Eco-hydro­log­i­cal stud­ies are highly empha­sized world­wide at the moment espe­cially where hydrau­lic struc­tures such as dams are con­cerned, mainly focus­ing on ben­e­fit­ing both humans and exist­ing eco­system for the pres­ent and future gen­er­a­tions. The study at Pan­gan­i basin was aimed at assess­ing the suf­ficiency and the amount of flow reach­ing the down­stream area of the Pan­gan­i River for main­te­nance of eco­sys­tem. Fish spe­cies were con­sid­ered as the indi­ca­tors for eco­sys­tem health. Flow dura­tion curves (FDC) and hy­dro­graphs were devel­oped by using the col­lected his­tor­i­cal daily flow data and used for assess­ing the flow var­i­a­tion before and after Ny­umba ya Mun­gu (NYM) dam con­struction. The results showed that there is no sea­son­al­i­ty and that for most part of the year the flow is within 20–40m3/s. From the com­par­i­son it was found that there is 42.7% decrease in Q5, 2.1% decrease in Q95, 38.9% increase in Q75, 23.4% increase in Q50 and decrease of per­cent­age ex­cee­dence of 50m3/s by 61.5%. Phys­i­cal hab­i­tat sim­u­la­tion model (PHAB­SIM) was used for hydrau­lic sim­u­la­tion incor­po­rat­ing geo­met­ric and flow data col­lected in the field. From the sim­u­la­tions min­i­mum flow for hab­i­tat pro­tec­tion is about 15m3/s and for flood for­ma­tion flows should be greater than 50m3/s. Thus the required res­er­voir out­flow for sus­tain­able water resources man­age­ment at the NYM should fol­low the above spec­i­fi­ca­tions.