The West Coast had its first big rain storm of the year this week, dumping several inches in places and breaking rainfall records in L.A. Of course, when all that rain hits the ground it flows downhill to the ocean, picking up trash, pollutants and toxins on the way. All of this creates a "toxic soup" of pollution that can make you very sick.
According to Beachapedia:
First flush is the initial surface runoff of a rainstorm. During this phase, water pollution entering storm drains in areas with high proportions of impervious surfaces is typically more concentrated compared to the remainder of the storm. Consequently these high concentrations of urban runoff result in high levels of pollutants discharged from storm sewers to surface waters.
Your county Health Department recommends staying out of the ocean for 3 days after a heavy rain, as the high levels of bacteria and other pollutants can make you very sick.
Check out this picture of a plume of pollution and sediment at Doheny State Beach after a major rain event, making it one of the dirtiest beaches in the nation.