Scientists are finding pollutants after storms can stay trapped near shore longer than previously thought.
It is recommended to wait 72 hours after a storm before surfing or swimming in the ocean.
However, researchers with Scripps Institution of Oceanography in La Jolla found that waves can carry contaminants as far away as five miles.
The results of their study may lead to new advisories on re-entering the surf after it rains.
“The plume will stay along the coastline instead of going offshore,” said Sarah Giddings, a professor at the Scripps Institution of Oceanography. "Waves have the tendency to move things on shore and mix them vertically."
Pollutants in ocean water can come from storm drains and river overflow. The health effects on humans can range from infections to sickness and even death.
"This can happen at beaches near the Tijuana River, the San Diego River, the outflow from Mission Bay," said Giddings. "Freshwater drains to those and exists the ocean."
The study also said that these contaminants are carried for longer distances than once thought.
The potency of the contaminants was still enough to cause harm to human health up to five miles away from the point of entry into ocean water.
The study was motivated by health concerns at Imperial Beach caused by plumes from the Tijuana River.
Multiple swimmers and surfers, including the mayor of Imperial Beach, Serge Dedina, have reported sickness after swimming in the ocean there.
Giddings warns that some bodies of water in the county, like Los Peñasquitos Lagoon, can still carry contaminants even without a storm.
That’s due to runoff from people watering their lawns or washing their cars in the area.
It is recommended that people wait 72 hours after rainfall before getting into the ocean again.
However, with the new research, Giddings added that recommendation could be extended after further testing is concluded over the next few months.