Limited water resources in semi-arid regions can create a heavy public demand to use available water storage lakes for multiple use recreational purposes. Since bacteriological measurements of recreational water quality must be based on the detection of fecal contamination by all warm-blooded animals, this paper offers a rationale for the fecal coliform concept with respect to: sanitary significance, density relationships with fecal streptococci, and illustrates a bacteriological approach to a study of water quality in Buffalo Lake. Buffalo Lake, 30 miles (48 km) southwest of Amarillo, Texas, is part of a national wildlife refuge with authorized recreational uses in specified zoned areas to include swimming, water skiing, fishing, boating, and camping. Source water is derived from a drainage basin receiving only 15 in. (38.1 cm) of rainfall per year and supporting a human population of approximately 15,000 persons and a cattle feedlot population of approximately 180,000 animals. During the prevailing long dry weather periods the natural bathing water quality in the lake is excellent, as illustrated during a 1-week period (June 1968) when the fecal coliform median value from all 48 samples collected at six locations was 7 organisms per 100 ml. Stormwater runoff produced by infrequent heavy thunder-showers results in a dramatic deterioration in water quality for feeder streams, and subsequently produces a bacteriological impact on Buffalo Lake water quality which may be seen in fecal coliform values far in excess of the 200 organisms per 100 ml limit recommended by the National Advisory Committee on Water Quality Criteria. Corrective measures are discussed to more adequately control the pollutional discharges from domestic sewage and cattle feedlot drainage that reaches the lake, in addition to restrictions on bathing and water skiing when inflow from source waters temporarily reaches more than 450 acre-ft (5.6 × 10 5 m 3) as a result of stormwater runoff; restrictions on horsepower limit and total number of motorboats, plus continuous maintenance and enforcement of a buffer zone between the wildlife refuge area and those areas of the lake designated for swimming, wading, and skiing.