Heal the Bay publishes an annual Beach Pollution Report Card which reports on water samples taken regularly along the beaches of Santa Monica Bay (most are taken weekly, with some daily during the summer season). An "A" rating means unhealthy bacterial levels are reached less than 5% of the time, "B" means unhealthy bacterial levels are reached 5%-10% of the time, "C" means unhealthy bacterial levels are reached 10%-25% of the time, "D" means unhealthy bacterial levels are reached 25%-40% of the time, "F" means unhealthy bacterial levels are reached more than 40% of the time.
The chart shows the drastic differences between wet weather (52% unhealthy) (during which the rain washes much pollution from streets and yards into the bay) and dry weather (only 15% unhealthy) (with pollution sources such as over-flowing septic tanks). te that water quality drops during and immediately after a rainstorm, but often rebounds to its previous level within a few days, meaning that most of Santa Monica Bay is safe to swim in, except during the three days following a rain. One should also avoid all storm drains and certain streams, such as Ballona Creek and Malibu Creek.
The Santa Monica Bay Restoration Project recently issued an epidemiological study of the risks of swimming in the Bay near drains with a high bacterial count. The study found that one's risk of respiratory and other diseases nearly doubles in the presence of bacteria, causing hundreds of cases of illness per every 10,000 swimmers.