The main purpose of the beach monitoring program is to protect public health by providing timely information about the water quality at public swimming beaches on lakes Sammamish, Washington and Green Lake. The primary method used to accomplish this is by routinely sampling E.coli and fecal coliform bacteria, and sampling for cyanobacterial toxins (beginning 2005 for two years) during bloom events. The program also provides additional data that can be used to help identify the source of bacteria, whether from bathers, animals or overflow from the sewage collection and conveyance system. This program implements a plan to coordinate roles of inter-departmental agencies involved in water testing, public health assessments, beach closures and media response. The bacterial data are collected weekly during the swimming season (mid-May through mid-September) and are posted on the King County swimming beach web page.