A study was conducted at two beaches on Lake Erie to evaluate the water sampling design for the collection of several microbiological indicator organisms in relation to day, time, and location of collection. The concentrations of these organisms were generally found to vary significantly (P < 0.05) by the specific time of day and day of weekend that collection took place. However, the concentrations of these organisms did not vary significantly (P > 0.05) at various locations in the bathing area. Future studies investigating the health effects of recreational water as related to microbiological variables should be designed to collect water samples at the specific time of day and day of weekend that an individual was exposed. In addition, sampling at various locations in the bathing area should probably be considered for those beaches having poor dispersion of fecal waste sources. (Am J Public Health 1981; 71:283-289.)