The water quality of Sheshroodbar River in Savadkooh was studied with population indices of benthic macroinvertebrates through sampling in 12 intervals at five stations in three replications, along with measuring some physicochemical parameters during 2014-2015. Among the invertebrates of the river (16 families from seven orders and six classes, n = 5230), aquatic insects larvae had the highest diversity. Significant differences were found between EPT and EPT/CHIR indices at different stations (p ≤ 0.05), but Shannon and Hilsenhoff indices were not significantly different among stations (p ≥ 0.05). Diptera at stations 1 and 2 and Diptera, Ephemeroptera, and Trichoptera at station 3 (n = 202, 256, & 282, respectively) showed the highest annual mean abundance. Mean annual frequency of orders was maximum for Haplotaxida, Tubificida, Lmbricida, Lumbriculida, Oligochaeta and Ephemeroptera at station 4, and for Trichoptera at station 5. The highest (12.3 ± 0.11) and the lowest (1.66 ± 0.24) annual averages of the Shannon-Wiener index were estimated for stations 1 and 4, respectively. The annual water quality was found to be very good (3.99 ± 0.18) to moderate (5.21 ± 0.21) from station 1 to station 3 (upstream to middle stations). Annual water quality was relatively poor (6.11 ± 0.34) downstream of station 4 while it was fairly good (4.55 ± 0.39) at station 5 due to the river self-purification. With changes and stresses of the river, increased and relatively decreased frequencies were observed in resistant and susceptible groups of the macroinvertebrates, respectively.
