A REGIONAL SURVEY OF THE MICROBIOLOGICAL WATER QUALITY ALONG THE SHORELINE OF THE SOUTHERN CALIFORNIA BIGHT RACHEL T. NOBLE 1,3 , JOHN H. DORSEY 2 , MOLLY LEECASTER 3 , VICTORIA OROZCO-BORBÓN 4 , DANIEL REID 5 , KENNETH SCHIFF 3 and STEPHEN B. WEISBERG 3 1 Wrigley Institute for Environmental Studies, University of Southern California, Los Angeles, CA 90089 USA; 2 City of Los Angeles, Stormwater Management Division, 650 S. Spring Street, Los Angeles, CA 90014 USA; 3 Southern California Coastal Water Research Project, 7171 Fenwick Lane, Westminster, CA 92683 USA; 4 Instituto de Investigaciones Oceanologicas, Universidad Autonoma de Baja California, Ensenada, Mexico; 5 Santa Barbara County Public Health Department, 225 Camino Del Remedio, Santa Barbara, CA 93110 USA Abstract. A regional survey of the microbiological water quality along the shoreline of the South- ern California Bight (SCB), from Point Conception south to Ensenada, Mexico, was conducted dur- ing August, 1998, by 36 agencies under the coordination of the Southern California Coastal Water Research Project (SCCWRP). Microbiological water quality was assessed by calculating the per- centage of shoreline-mile-days that exceeded bacterial indicator thresholds for total and fecal coliforms, total/fecal ratios, and enterococci. Sample sites were selected using a stratified random sampling approach, with the SCB recreational shoreline divided into six strata: high- and low-use sandy beaches, high- and low-use rocky shoreline, and perennial and ephemeral freshwater outlets. Samples were collected on a weekly basis at a total of 253 sites, beginning on August 2 nd , 1998 and continuing for five weeks. Samples were analyzed by 22 participating labs using their normal meth- ods (multiple tube fermentation, membrane filtration, Colilert® and/or Enterolert®). All labs met testing criteria established through intercalibration exercises and quality control check samples dis- tributed during the sampling period. Nearly 95% of the shoreline-mile days did not exceed daily and monthly bacterial indicator thresholds, demonstrating good bacteriological water quality along the SCB shoreline. Freshwater outlets, comprised mainly of storm drains, had the poorest water quality with 60% and 40% of the shoreline-miles exceeding monthly and daily thresholds, respectively. Freshwater outlets were also more likely to demonstrate exceedances by multiple indicators at a single site, and repeat exceedances at sites over the five-week period. Compared with the southern California beaches, Mexican beaches had nearly 5 times the number of exceedances for total and fe- cal coliforms, and nearly 8 times the number of exceedances for total/fecal ratios. Keywords: regional survey, water quality, indicator bacteria, total and fecal coliforms, enterococci 1. Introduction The Southern California Bight (SCB, Figure 1), stretching from Point Conception southward to Cabo Colnett, Baja California, is a world-renowned recreational re- source. Southern California beaches annually attract more than 175 million people to sunbathe, surf, swim, and skin- and SCUBA-dive (USLA 1998). This region is densely populated, with nearly 20 million people inhabiting coastal areas, a num- ber that is projected to increase 20% by the year 2010 (NRC 1990). With such ac- Environmental Monitoring and Assessment 64: 435–447, 2000. c 2000 Kluwer Academic Publishers. Printed in the Netherlands.