Methods of collecting, concentrating, separating, and identifying organic compounds in natural water systems are presented. These methods were applied to a eutrophic reservoir (Hyrum Reservoir, Utah) and resulted in the identification of the following 27 volatile, organic compounds: Alcohols: methanol, ethanol, 1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 2-methyl-l-butanol, methyl-1- butanol, 3-methyl-2-butanol, 2-methyl-2-butanol, 2-methyl-3-buten-2-ol, 1-penten-3-ol, 2-methyl-2-pentanol Ketones: acetone, methyl ethyl ketone, 4-methyl-3-penten-2-one Aldehydes: acetaldehyde, propanal, 2-buten-1-al Others: acetonitrile, ethyl acetate, pyridine, 3-methylpyridine, diethyl ether The concentration level of the following 13 compounds was established in the reservoir from October 1974 to January 1976: Alcohols: methanol, ethanol, propanol, isopropyl alcohol, 1-butanol, isobutyl alcohol, tert-butyl alcohol 2-methyl-2-butanol, 2-methyl-3-buten-2-ol Ketones: acetone, methyl ethyl ketone Others: acetonitrile, acetaldehyde The highest concentrations of organics were found in the late summer or early fall as the bloom of Aphanizomenon flos-aquae died and the level of bacterial fermentation increased. Other sources of organic compounds in the reservoir (besides fermentation) included compounds (acetonitrile and ethanol) at least partially produced by active algal growth and associated bacteria. Melting snowpack and mountain streams that feed the reservoir also contained organic compounds similar to those found in the reservoir, however at lower levels. Most of the compounds at low concentrations had no effect on the growth of certain algae tested, however there was some indication that certain organics may have increased the net growth of Aphanizomenon flos-aquae.