The Selenga River, a major tributary of Lake Baikal in Russia, was studied to assess water quality using aquatic insects as indicators. The insects showed sensitivity to pollution, with lower scores near areas like Ulan-Ude city's wastewater discharge and mining operations at Zakamensk. However, the ecosystem showed signs of recovery within a few kilometers downstream of pollution sources. Natural factors like water flow and sediment type also influenced insect communities. The study provides a map of insect distribution in the Selenga delta.