San Diego's water is getting turned pink to see how beaches get contaminated

Bacteria, chemicals and trash often end up on SoCal beaches after it rains. To understand how this and other contamination ends up in the water, the Scripps Institution of Oceanography at UC San Diego is dying water pink. 

"We're doing it for a variety of reasons, but I think one of the big reasons is to try to understand how and where and when our beaches are contaminated," Sarah Giddings, assistant professor at Scripps, told KPCC. "In Southern California we have multiple cases where beaches have to be closed. For example, maybe a sewer main breaks."

The dye acts like a pollutant would in water, becoming something like a tracer in the surf zone. Researchers are "able to use the dye as sort of a marker to know where thing are going," Giddings said. 

Researchers have released non-toxic bright pink fluorescent dye into beach waters and tracked its movements along the coast. (Photo: Scripps Institution of Oceanography, UC San Diego)

The pink dye is brightest within the first six hours after it's released. It stays visible to the eye for the first 24 hours, then that, it becomes more difficult to see. It is both EPA and FDA approved, Giddings said. The dye is also used in drinking water studies. 

The study is supposed to help better predict where and when different areas are at risk. "We track the dye and learn about the physics of the processes that drives the movement of the dye," Giddings said. "For example, the competition between waves breaking on the shore and moving dye around versus wind blowing on the surface and moving dye around."

Giddings said there is a difference in movement depending on if the object is active or passive. The study looks at the movement around passive particles. "We know that's a big component of what moves things like sediments, larvae pollutants, around in the ocean, and so we're examining that component of it," she said.

Scripps tests the movement of pollutants, but the study also helps researchers see how fish larvae move.

The beach area where the study was done, south Imperial Beach to Coronado, is relatively straight, said Giddings. "That gives us an idealized beach condition that can then be thought of as applying to beaches, really all over the world."

One of the dye releases happened this week. The next two dye releases are set to happen between now and Oct. 17. Giddings said that, in the end, she hopes the study brings a better understanding of the pollutant transportation that happens in the surf zone and between the surf zone and offshore.

"We would like to, in the long term, use this data to help guide our modeling so that we have good models that can help predict when there might be problematic areas along the beaches," she said.