Sunscreen Slicks & the South Yuba

Share with Your People

The recent warm temperatures have motivated people to find their way to the Yuba so they can cool off in the refreshing emerald waters. Our River Ambassadors saw about 1000 people at Bridgeport and Highway 49 this past weekend just between the hours of 10am and 2pm.

This weekend’s heat wave will likely create an even greater surge in visitors as temperatures are predicated to climb into the triple digits starting on Thursday.

Over the past several weeks, our River Ambassadors have been fielding questions from river-goers about a slick they are seeing on the water. While an oily film on the water can be the result of anything from gas to naturally occurring iron-oxidizing bacteria, the film people are reporting is at busy river crossings where hundreds are congregating at any given hour, meaning that it is likely sunscreen.

Many of the thousands of people who visit the river apply sunscreen before they take a dip to protect themselves from sunburn. Sunscreen often contains chemicals that help block UV rays, including oxybenzone and octinoxate. 

River Ambassadors on Memorial Day weekend (Photo: SYRCL staff)

Studies have found that these chemicals (along with other chemicals commonly found in sunscreens) can travel to the ocean where they can cause coral bleaching. As a result of this research, sales of sunscreens containing these two chemicals have been banned in Hawaii since 2018.

What does this mean for the Yuba? 

According to a 2020 study, UV-blocking chemicals such as avobenzone, oxybenzone, and octocrylene are not just damaging coral, they are also lethal to some freshwater organisms. Researchers found that they can kill the water flea, Daphnia magna, an important link in freshwater food chains that, when removed, “could cause the local ecosystem to collapse,” according to lead author, Aaron Boyd.

Another study showed that the chemicals in sunscreen negatively impact the growth of certain freshwater plant species, including milfoils that provide important food sources. Again, such impacts reverberate all the way up the food chain.

While much more research has yet to be done, existing studies suggest that sunscreen is negatively disrupting freshwater ecosystems and causing decreased fertility and reproduction in some fish. 

People recreating at the Highway 49 crossing on Sunday, June 13 (Photo credit: SYRCL staff)

What can you do?

Wear clothing with a UPF rating.

Lightweight shirts and pants combined with a full brimmed hat are a great way to protect yourself from the sun. Of course, these are not the best choices for swimming. You can also try second skin shirts, which are made to go in the water.

Use a more environmentally friendly sunscreen.

Products labeled “reef-safe” or “reef-friendly” do not have agreed-upon definitions. Further, the FDA does not regulate the use of this terminology.

Thus, the best way to go about selecting less harmful sunscreen is to flip the bottle over and make certain it does not contain oxybenzone, octinoxate, or octocrylene. NOAA also lists the following chemicals as ones to avoid: benzophenone-1, benzophenone-8, OD-PABA, 4-methylbenzylidene camphor, 3-benzylidene camphor, nano-titanium dioxide, nano-Zinc oxide.

Mineral-based sunscreens are typically a good option. If you do go with zinc oxide or titanium oxide, make certain it is not nano-, which contains small particles coral reefs “breathe” in that can damage them.

Make certain your sunscreen of choice is highly water resistant.

Sunscreens marked as highly water resistant do not dissolve immediately in the water, protecting both your skin and the river better.

Follow the directions on the sunscreen bottle.

Some sunscreens advise that you wait a designated amount of time after application for it to take full effect. This ensures the effort you took applying the sunscreen won’t be for naught when you decide to cool off in the water.

Share with Your People

Did you enjoy this post?

Get new SYRCL articles delivered to your inbox by subscribing to our ENews.


  1. Yes, or at least sunscreen should be banned from use at the river. I don’t think most people will make the effort to comply to these guidelines you lay out, and most who swim in the Yuba will never even read this. Signs at the river may help, but probably only a small percentage of people who read them will actually change their behavior.

    1. Betsy Brunner says:

      Thank you, Maria. We are working to extend the messaging to the public via our River Ambassadors program.

  2. Would it be possible for the river ambassadors to sell small bottles of sunscreen that is more environmentally friendly?

Comments are closed.