Several advantages of utilizing microbial communities, particularly protozoan communities forming on artificial substrates, in the assessment of pollutional stress are discussed. The process of community formation on artificial substrates is likened to that of island colonization, and the means of analyzing and interpreting variations in the dynamics of species accrual are presented. Results from a study conducted in Smith Mountain Lake, Virginia, illustrate how the colonization process reflects characteristics of both the composition and the productivity of the source species pool–the natural protozoan community.