The aerated lagoon method of wastewater treatment is primarily a product of the 1960's. The effect of climatic conditions is especially significant in the colder Northern regions where ice problems, which appeared in the first installation treating domestic wastewaters, become serious and have threatened the very idea of aerated lagoons as a practical method of biological treatment in these climates. The first aerated lagoon in Alaska, constructed in 1967 was located at the Eielson Air Force Base near Fairbanks. By 1970, there were at least 17 aerated lagoons in Alaska. All except one of these units were using perforated tubing diffused aeration for oxygenation and mixing. This aeration method was largely accepted to prevent reoccurrence of the bad icing experiences reported with mechanical surface aeration at other Northern installations. With regard to differences among biological treatment processes operating in cold climates the most important factor from a biological point of view is the effect of temperature upon the rate of biological reactions.