Collections of stream organisms from a domestic water supply system adjacent to the Tobacco River revealed that a detritus-based community exists in subterranean waters circulating through floodplain gravels at least 4.2 meters below and 50 meters laterally from the river channel. Several stone fly species spend their entire nymphal life cycles in underground habitats of the Flathead and Tobacco rivers.

Year-round field studies of the biology of stream sanitation were initiated by the biology section of the Public Health Service's Environmental Health Center on Lytle Creek in October 1949. The aims of these investigations were: 1. To develop or devise and field test procedures and equipment for biological surveys and investigations of polluted streams. 2. To investigate seasonal and diurnal environmental changes in a stream polluted with oxygen-depleting wastes. 3. To determine how the physical-chemical environment in the various pollutional zones affects the qualitative and quantitative composition of aquatic populations and how these populations in turn affect or change physicalchemical conditions. 4. To relate various qualitative and quantitative compositions of aquatic populations to environmental conditions found in streams polluted with organic wastes and to test the value and use of aquatic organisms as indicators of clean water and various degrees of pollution at all seasons of the year. 5. To determine the rate of satisfaction of biochemical oxygen demand (BOD), the area in which most of the demand is satisfied, and how seasonal and other environmental conditions affect the process. 6. To determine the value of fishes as indicators of pollution and their use in evaluating the effects of pollution.

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Collections of fish were made in LytleCreek, Clinton County, Ohio, to determine the effect of the partially treated domestic sewage of Wilmington, Ohio, on the fish populations of this stream. The farther the collecting localities were downstream from the plant effluent, the greater were the numbers of species and individu.als found. In the septic areas, immediately below the effluent, no fish were observed or collected. Two miles below, in the recovery zone, an average of 1.2 species and 2.2 individuals were taken per collection, with 8 different species represented. Three miles below, also in the recovery zone, 12 species were represented in our collections, with a mean of 1.7 species and 10.8 individuals per collection. In the lower portion of the recovery zone, 4.4 miles below the effluent, 32 species were taken, with a mean of 12.7 species and 197 individuals. In the clean-water zone, 36 species were taken, with a mean of 16.7 species and 294 individuals. No species could be used as indicators of pollution although several were relatively tolerant of unfavorable conditions. The various species of darters and black bass were highly sensitive and their presence was usually indicative of favorable conditions. During the winter when the stream flow was at a maximum and the dissolved oxygen was adequate in all sections of the stream, the fish failed to move into the areas they found intolerable during the summer periods of low flow. 157 DESCRIPTION OF LYTLE CREEK Lytle Creek lies about 45 miles northeast of Cincinnati, in Clinton County, Ohio, and flows into Todd's Fork, which is part of the Little Miami River system. It is a permanent stream, approximately 11 miles long, 3 to 35 feet wide during low-water stages, and drains a watershed of about 27 square miles. The depth of the stream varies from a few inches in the riffles to more than 6 feet in a few pools. The average gradient is 25 feet per mile. The base level of Lytle Creek lies within a meander belt of alluvial origin, the Genessee silt loam. The stream runs through Wisconsin glacial till, except for a short section located about 3 miles from the mouth, where it cuts down to Ordovician limestone. The principal sources of flow are drainage from adjacent agricultural areas and the effluent of the Wilmington Sewage Treatment Plant, which enters the stream about 7 miles above its mouth. The Sewage Treatment Plant serves the 7,000 inhabitants of Wilmington, Ohio, a non-industrial community. The sewage is treated by a chemical precipitation process, which removes most of the solids and reduces the biochemical oxygen demand of the wastes by about 50 percent. By the time the partially treated wastes are discharged to the stream, decomposition is well advanced, and little or no dissolved oxygen is present in the plant effluent. During normal low flows, the effluent comprises 80 to 90 percent of the total stream volume, causing septic conditions immediately below the outlet.Lytle Creek is deemed particularly favorable for study because it has only one major source ...