72-Hours: Post-Rain Pollution in the Surf Zone

Runoff from the Tijuana River is spread along shore by the current and wave activity. Photo: Deniz Ozakccay/wildcoast.net
Runoff from the Tijuana River spreads along the coast by way of current and wave activity. Photo: Deniz Ozakccay/wildcoast.net

72-Hours: Post-Rain Pollution in the Surf Zone

On Christmas Day, Barry Ault—a 71-year-old waterman and San Diego surfing legend—died a few days after paddling out at his home break near Sunset Cliffs. The cause of death was an acute Staph infection developed from the MRSA pathogen, which doctors believe he contracted from contaminated water by entering the surf zone too soon after a rain shower. Most Southern Californian ocean-goers know the 72-hour rule—a general guideline (often disregarded) that discourages people from entering the ocean within three days of rainfall to avoid getting sick from runoff pollution. But with the severity of Ault’s case, a lot of people are wondering: just how dangerous is the water near major metropolitan areas post-downpour?

“It really depends,” says Falk Feddersen, nearshore physical oceanographer and acting professor at the Scripps Institution of Oceanography. “There are so many variables, it’s impossible to make sweeping assumptions regarding what’s safe and what’s not.”

It is probable, however, that most coastal waters (particularly those fringing urban areas) are contaminated to some degree with a variety of illness- and disease-causing organisms, commonly referred to as pathogens. Most diseases associated with runoff pollution come from enteric pathogens—organisms that reside in the humans’ intestines that enter the surf zone via leaky sewage pipes. Swimmers and surfers who expose themselves to enteric pathogens are susceptible to the gamut of illnesses spread through ingestion of fecal-contaminated water. Among the most severe possibilities are E. Coli, Salmonella and even AIDS. But according to Chad Nelsen, environmental director at the Surfrider Foundation, most surfing-associated diseases come from viruses, which can cause gastroenteritis, hepatitis, respiratory illness, as well as ear, nose, and throat problems.

Other microbial pathogens found at varying concentrations in recreational waters include amoeba and protozoa, which can cause giardiasis, amoebic dysentery, skin rashes and pink eye,” Nelsen told Surfline. To gauge how long and how intensely these pathogens maintain their threat, scientists examine the physical distribution of matter near shore, which is where Falk Feddersen’s work comes into play.

Feddersen’s research focuses primarily on the dynamics of water near shore—how water transfers and dilutes pollution via wave activity, tide, currents and the bathymetry of the ocean floor. He says the coastline is divided by physical attributes that can stagger the effects of runoff pollution so that even neighboring beaches may see different levels of contamination post-rain.

“If you were to take a water sample from La Jolla Shores, where waves rarely get above ankle-high and the water generally sees less movement,” Feddersen says, “You’re likely going to see completely different characteristics than you would, say, just down the beach at Scripps Pier, where the waves can get bigger and the water is constantly circulating. Conditions may be completely safe at the Pier, when at the same time water at Shores could be contaminated. ”

To evaluate the spread of pathogens in the ocean, such as the MRSA pathogen that caused Ault’s death—whether he caught it in the water or not—Feddersen and his research team perform studies in which they release pink dye into the ocean and track its movement with a bird’s-eye view of the shoreline. The travel and spread of the pink dye, which plumes along shore and out to sea by way of currents and wave activity, indicates how pathogens might also travel and spread once they reach the ocean.

“What we see is that areas with more wave activity and water movement spread things farther and more rapidly, but also dilute them quicker,” Feddersen says. “But at the same time, if we were to release the dye in a large bay or an area with less circulation, it would stay more concentrated and confined mainly to that area.”

falk feddersen
Researchers release pink die into the ocean around Scripps Pier to study the movement of pathogens after rainfall Photo: David Clark/falk.ucsd.edu

The pink die may reflect the movement of illness-causing pathogens, but it doesn’t reflect other variables, like the facts that pathogens can also die and procreate. Dilution is one component in determining an area’s potential for contamination, but so is sunlight, temperature and an array of other factors that effect the proliferation or deterioration of pathogens. What they find is that contamination exists on a case-by-case basis, it’s random and no sweeping general rule really applies to all coastlines, or even all of Southern California. Some places may need up to 72-hours to safely dilute contamination. Others may need more, others may need less. Others may not be contaminated at all.

“There’s no scientific evidence to validate the 72-hour rule specifically,” Feddersen says, “That doesn’t mean it’s not valid, but it’s impossible to tell how much and for how long a given area is subject to contamination, if it even is contaminated. It’s more of a general precaution, particularly for areas near urban zones and runoff zones.”

So what does all this mean when the clouds pass and the waves are firing? Should an ocean goer turn down water time for fear of poo particles and pathogens?

“In areas close to heavy runoff deposits, such as Imperial Beach (which sits just North of the Tijuana slough) or Sunset Cliffs (just south of the San Diego river deposit), it’s probably better to wait,” Feddersen says. “But you can also get MRSA (or another harmful pathogen) from the bench press machine at your local gym. Evaluating safety is more about understanding the conditions and the physical nature of a given spot.”

Cases like Ault’s are anomalous and shouldn’t inspire fear, but they should deliver caution. If the water smells weird, if it burns or tastes funny, if there is visible fecal matter, don’t go. Use your better judgement when considering the runoff around your zone after a rain. And after it clears, paddle like it’s gonna rain tomorrow.

For more info on Barry Ault’s death and the runoff pollution debate, click here.

For more about the 72-hour rule, click here.

To see more about Falk Feddersen’s research, click here.

For more on efforts to clean up our waterways, click here.