A rich fauna of Ephemeroptera (mayfly), Plecoptera (stonefly) and Trichoptera (caddisfly) (EPT) were collected from 14 highland streams discharging into the Temenggor Reservoir in Perak in the northern peninsular Malaysia. Out of the 3 orders, Ephemeroptera was the most diverse but Trichoptera was the most abundant. 45 genera that belonged to 25 families of EPT were recorded. Distribution of EPT varied significantly between orders and types of streams they inhabited. Their diversity and abundance were higher in the second and third order streams. There was no significant relationship between environmental parameters and diversity as well as abundance of EPT in these streams. Their diversity indices together with EPT taxa richness scores referred to clean water environment, hence very suitable for these insects. The EPT taxa richness calculated for the 14 streams reflected that 13 out of 14 streams were undisturbed having good water quality (value of EPT taxa richness ＞ 10). Previous logging and mining activities were suspected to be the main cause for tremendous disappearance of EPT genera in the Kelian stream. Since no previous human activities were recorded around the Telang stream, natural phenomena possibly contributed to low abundance of these insects in the Telang stream.