This article discusses an episode of mustiness that was extremely resistant to treatment processes, which occurred on the Cedar River in Iowa during June through July, 1961. A study was done on the chemical characteristics of the metabolic products of actinomycetes isolated and cultured from the Cedar River during the 1961 period of musty taste. The difficulty of analysis, effect of cultural conditions, isolation procedures and actinomycete‐produced substances are all discussed, along with neutral‐fraction characteristics, further purification, constituents of eluate, and infrared analysis. An illustration of the similarity between organic materials of river water and extracted actinomycete metabolites is provided in a comparison of the infrared spectra of an extract of musty Cedar River water, and an extract of the laboratory‐cultured actinomycetes.