Water managers drop the ball on Hetch Hetchy

Hetch Hetchy Reservoir has been covered with floating black balls to reduce evaporation and protect water quality

By Nan W. Frobish

Visitors to Yosemite’s iconic Hetch Hetchy reservoir are doing a double-take. Instead of seeing the majestic backdrop of the Sierra Nevada reflected in the pristine mountain water, they are now greeted by millions of black balls that cover the surface.

After four years of record-setting drought and statewide low reservoir levels, concerns developed about evaporation losses and the drought’s effect on water quality for San Francisco’s premier water source. Plans to protect the drinking supply and reduce reservoir evaporation began in 2014, when another year of dry conditions was predicted with no end to the drought in sight.

Inspired by similar measures taken at Ivanhoe Reservoir and the Los Angeles Reservoir in Southern California, 96 million black balls were poured into Hetch Hetchy to limit sunlight penetrating the water surface. Limiting sunlight on the reservoir will reduce both evaporation and the growth of potential contaminants. Given the emergency measures required to mitigate the drought’s effects on municipal water supplies, covering the reservoir was deemed more cost-effective and easier to achieve than constructing additional treatment facilities or implementing additional water conservation actions.

Milly Pore, a spokesperson from the San Francisco PEC, explained, “We are facing long-term concerns about water quality and water supply reliability and estimated that we could save a lot of water and water quality this way.”

“It’s an eye-sore,” said Louie Swan, a recent visitor to the reservoir. “It looks like an oil slick. If this is the best we can come up with to fix water quality, we might as well take the dam down altogether.”

Average 2100 deliveries, scarcity, and scarcity cost associated with O'Shaughnessy Dam removal

Average 2100 deliveries, scarcity, and scarcity cost associated with O’Shaughnessy Dam removal. Null and Lund (2006)

Previous research suggests that dam removal may be a contentious idea whose time has come for the politically charged reservoir. Dr. Sarah Null, a former researcher at the Center for Watershed Sciences, published a study of the effects of dam removal on San Francisco’s water supply. The findings suggest that the dam could be removed with little loss to water supply, but would require additional water treatment costs.

With more and prolonged droughts predicted due to climate change, those water treatment costs are becoming a reality. As water managers and conservationists are becoming aware of the “new normal” for water quality in Hetch Hetchy, dam removal is quietly being revisited.

Hetch Hetchy Reservoir, before black balls were used to cover the water surface

Hetch Hetchy Reservoir, before being black balled

Hetch Hetchy Valley, before O'Shaughnessy Dam was constructed

Hetch Hetchy Valley, before O’Shaughnessy Dam

“It’s a sensitive issue,” said one state agency representative with knowledge of the dam removal talks. “Frankly, we never thought the barriers to dam removal would [be eliminated] by natural conditions. But now that they are, it gives dam removal advocates a stronger position.”

As awareness grows of the recent management activities, local San Francisco residents are voicing additional concerns.

“What are the balls made out of, anyway?” asked Matthew McPhee, a long-time Bay Area resident who was attracted to the city because of its environmental consciousness. “Are they BPA-free? Will sunlight degrade their material? We’re just trading one water quality issue for another.”

The materials used in each black balls are causing some Bay Area residents to question their net effect on water quality

The materials used in each black balls are causing some Bay Area residents to question their net effect on water quality. Photo credit: Irfan Khan, Los Angeles Times

As well as addressing water quality issues, the ‘shade balls’ are also a pilot project to address broader goals set by Governor Brown to reduce evaporation in all of California’s reservoirs.

“Following last year’s 25% reduction in urban water use, we considered requiring that all reservoirs be covered to further save water,” says Rex Kransrose of the Governor’s office. “This year’s wetter conditions delayed this move, but we are glad to see San Francisco leading the way on this.”

“Water supply losses due to evaporation are a major issue,” says Dr. Mollie Luna, a researcher at the Center for Watershed Sciences. “We have enough storage, it’s preventing loss that’s the issue. We’re not sure how effective these shade balls might be, but the drought has shown us that we need to proactively consider many different approaches to secure our water supply.”

Recreational activities bump up against the black ball approach. Image source: www.amusingplant.com

Recreational activities bump up against the black ball approach. Photo credit: Gerd Ludwig, National Geographic

Balancing the ‘shade balls’ with recreational uses is another concern. One option is to phase out municipal supply from reservoirs with the poorest water quality, and gradually transition to solely recreational purposes. The experiment on Hetch Hetchy will provide guidance on whether the ‘shade ball’ approach can be effective for California’s extensive reservoir system.



Nan W. Frobish is an occasional contributor to the California Waterblog and director of life enrichment for the UC Davis Center for Watershed Sciences.

Further reading

A reservoir goes undercover. Los Angeles Times. June 10, 2008

Why Did L.A. Drop 96 Million ‘Shade Balls’ Into Its Water? National Geographic. August 12, 2015

Magin, G.B. and L.E. Randall (1960), Review of Literature on Evaporation Suppression, US Geological Survey, Professional Paper 272-C, U.S. Govt. Printing Office, Washington, DC.

Null SE and Lund JR. 2006. Reassembling Hetch Hetchy: Water supply without O’Shaughnessy Dam. Journal of the American Water Resources Association, Vol. 42, No. 4, pp. 395 – 408, April 2006.

Null, Sarah E., 2016. Water Supply Reliability Tradeoffs between Removing Reservoir Storage and Improving Water Conveyance in California. Journal of the American Water Resources Association (JAWRA) 1-17. DOI:10.1111/1752-1688.12391.

This entry was posted in April Fools' Day, Uncategorized. Bookmark the permalink.

23 Responses to Water managers drop the ball on Hetch Hetchy

  1. Corentin girard says:

    Nice cost-effective solution, but what about the fishes, will they get hooked. In France, we worry about a specific fish that reproduce at the beginning of April (the famous poisson d’avril!).

    Good to know that you take care of him.

    Thanks for the post ; )

    • jaylund says:

      There was some concern about the spawning of this fish, but it is an abundant species. Some on the team of biologists felt that the cover provided by the balls would likely reduce predation by birds, although there is some concern that the balls will stick to the backs of these fish.

      • Michel Fortin says:

        Not so funny April fools. haha.

      • stan says:

        Why not let corporations put their logos on the balls for a fee, and use that revenue to pay for the project? Seems like a missed opportunity.

  2. Michel Fortin says:

    While the rest of the world moves towards removing plastic from the environment, is it prudent for California to take this action.

  3. Tony Wisneske says:

    THIS IS TERRIBLE! I’m starting a petition to get these balls removed immediately from our water system. Today’s environmentalists get it all wrong!

  4. Chuck says:

    And a happy April Fools Day to you too.

  5. gymnosperm says:

    White balls would work better, an aesthetic consideration? Those black balls are definitely going to warm the surface.

  6. Mark Fasi says:

    Has to be April Fools!!!

  7. Did you feel that? It wasn’t an ordinary earthquake, it was John Muir rolling over in his grave. Or was he laughing?
    From 1967:
    “Mr. McGuire: I want to say one word to you. Just one word.
    Benjamin: Yes, sir.
    Mr. McGuire: Are you listening?
    Benjamin: Yes, I am.
    Mr. McGuire: Plastics.
    Benjamin: Exactly how do you mean?
    Mr. McGuire: There’s a great future in plastics. Think about it. Will you think about it? ”

    ~koo koo kachoo

    • Lauren Padron says:

      Ha ha!!! Great comment. Poor Muir. Hopefully, some of us can still “see oceans in drops of dew.”

  8. Wes Skahnson says:

    I wouldn’t trust anything that Louie Swan character has to say. His love of chasing balls makes him a bit unreliable. 😉

  9. eagles and osprey are screwed can’t fish fish can’t surface feed ….someone needs to fire these idiots! I believe similar efforts were found ridiculous and caused water pollution’

    What is the carbon footprint of this crap and disposal – ?


  10. HA! “We might as well take the dam down altogether.” We know they’d never say that in the midst of litigation with Restore Hetch Hetchy. Must be an April Fools.

  11. Totally unwarranted to put plastic in an iconic glacier carved valley in Yosemite. Disrespectful. Get em out; every last one. (April Fool – good one)

    And while you’re at it, the dam and reservoir have no place in a national park either. Take them out as well.(No foolin’)

    • Kathleen Annette Wilson Raphael says:

      Is this for real. When do they remove the balls and how. This must be an unfunny joke.

  12. Finally, fullerenes to the rescue! At this rate the big drought will soon be history.

  13. Les Marsden says:

    Folks – this is a skillfully-written, beautifully-conceived APRIL FOOLS JOKE. And like all really great intellectual satire, it’s based upon certain truths. But those realities are easily distinguished from the further fantasies so well-developed and subtly mocked here. Let’s adopt just a tad bit of common sense before flying off into a tizzy, shall we? And perhaps it’s important to remember the not-too-old but nonetheless wise adage: just because it’s on the Interwebby-thingy, it’s not necessarily true.

  14. stan says:

    I had heard they were going to call the project Muir’s Balls. To honor a man who had the. The courage to co found the Sierra Club.

  15. Tommy Weaver says:

    So when are all those ball go when the reservoir spills ?

  16. khosro says:

    (96 million black balls were poured into Hetch Hetchy)
    In Los Angeles Reservoir they poured 96 million black balls. I think it’s not true for Hetch Hetchy because area in Hetch Hetchy is about 800 hectare that we need 920 million

Leave a Reply