Rain: This week’s wet weather was needed but still brought pollution to local shores. Andrew McNab

Everyone’s heard the advice: “Stay out of the water for a few days after it rains.”

From trash to oil to pet poop, the water off the coast of Santa Monica is swirling with bacterial, chemical and solid pollutants thanks to Tuesday’s rainstorm. Elevated levels of dangerous (and gross) bacteria like e.coli and Enterococcus can be tracked in coastal water for around 72 hours following any amount of rain, but even more so during an early-season deluge like the 1.56 inches that came down in Santa Monica this week.

While bacteria and trash are generally flushed out into deeper water after three days, some other pollutants, such as heavy metals and pesticides, tend to sink to the seafloor and remain in sediment for “a long period of time,” Heal the Bay water quality scientist Luke Ginger said.

“A lot of these contaminants just stay there, unfortunately,” Ginger described. But whereas bacteria pose immediate health threats, for metals and pesticides “it takes more chronic, long-term exposure in certain concentrations in order to become sick.” Still, giving more time for them to settle also helps protect you from exposure.

Ginger cautioned would-be beachgoers to consider skipping the visit this weekend or showering immediately after swimming.

Though all of coastal California deals with pollutant runoff during rain storms, Santa Monica’s storm drains have become notorious for delivering much of the county’s debris onto local beaches, particularly the Pico-Kenter Storm Drain.

“The first few big rainstorms, we call them ‘first flush’ events because they tend to wash pollutants that have built up over the dry season,” Ginger said. “They wash all those pollutants out in the ocean. All the pollutants that have accumulated over the summer get washed out in those first few storms. So, water quality in the ocean is actually a lot worse during the first few storm events than one you might get in February or March.”

The storm drain systems you can see gushing water out onto the beach during rain events are tied to the grates you’ll find on most street corners across Los Angeles and Santa Monica, Ginger described. The grates collect rainwater (as well as motor oil and organic and inorganic debris) throughout Los Angeles County, stretching like branches of a massive, 2,700-square-mile tree that culminate in one of the many storm drains dotted along the coast.

“If you were to start on the beach and walk–you know, tunnel–your way up a storm drain, it would quickly branch out in a bunch of different directions and you couldn’t really follow it to one specific place,” Ginger described, later adding that, in theory, “let’s say you’ve dumped your coffee out at the Hollywood Sign. That coffee would make its way into the storm drain system and out into the ocean. So, it’s all connected throughout the entire LA area.”

The Santa Monica-based nonprofit Heal the Bay tracks both wet and dry season beach bacteria levels and publishes information in its annual beach report card. According to Ginger, whose role includes studying pollution levels in ocean- and freshwater, California as a whole is showing slight improvement in its ocean water quality, although numbers fluctuate on a beach-by-beach basis–“The coastline is just so dynamic.”

“Unfortunately, we’ve seen some beaches get worse over time. And we’ve seen some beaches improve over time,” Ginger said. “But, but one thing we can say for sure is that in beaches that improve, we’ve seen the process of new regulations and restrictions put in place that lead to an improvement in water quality. We’ve seen that multiple times.”