The occurrence of mayfly (Ephemeroptera) larvae along the river Someş/Szamos

The distribution of mayfly (Ephemeroptera) larvae along the river Some? was studied from its spring to its mouth. We have found 18 species belonging to 4 different families. Knowing their density the collected mayfly species can be used as indicators of the water quality. The biodiversity (calculated with Shannon-Wiener formula) reached the maximum value (HS=I,502) at the first sampling point of the Some?ul Mare/Nagy Szamos (6 SM1). According to the lower biodiversity of mayfly larvae the river was very polluted downstream of big cities (Beclean. Násáud. Dej, Satu Mare)