The high manganese content contributed to the formation of a deep turbid layer dominated by stable manganese (40–65 m), which surrounds the redoxcline (~ 45–55 m) in the upper monimolimnion. This turbid layer in Lake Idro is described for the first time in this study. The article examines the distribution of dissolved and particulate forms of transition metals (Mn and Fe), alkaline earth metals (Ca and Mg), and other macro-constituents or nutrients (S, P, NO3-N, NH4-N), discussing their behavior at the redoxcline, where the main transition processes occur. Field measurements and theoretical considerations suggest that the deep turbid layer is formed by a complex mixture of manganese and iron compounds, with a prevalence of Mn(II)/Mn(III) in various forms, including dissolved, colloidal, and fine particles, which give the turbid layer an opalescent white-pink hue. Bacterial populations show clear stratification, with the upper aerobic layer dominated by the heterotroph Flavobacterium sp., the turbid layer hosting a specific microbiological pool dominated by Caldimonas sp., and the deeper anaerobic layer dominated by the sulfur-oxidizing and denitrifying Sulfuricurvum sp.. The occurrence of an abnormal surface coloration of the lake in August 2010 is also noted.