Surrounded by barren brown hills and cracked, dry clay, San Luis Reservoir was so empty this week that the nearly milelong, meandering path from the old high-water mark to the waterline could have doubled as a set in the post-apocalyptic “Mad Max” film franchise.
Down at the water, far below two dry boat ramps, Don Weber and Bob Lewis sat in lawn chairs beside their pickup. The fishermen, both from Carmel Valley, said they had not noticed that the wind-whipped water had a slightly green hue. Nor had they read the warning that state water officials issued a week earlier, recommending that people and their dogs stay out of the reservoir – the state’s fifth largest – because of potentially toxic blue-green algae.
“You sure can’t see it,” Weber said.
But the algae is there. In fact, so much is floating beneath the surface that it’s causing problems for the managers of Silicon Valley’s water supply. They’re battling foul tastes and smells caused by the algae, even after treatment renders the water safe to drink.
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The problems at San Luis Reservoir in Merced County are emblematic of a troubling number of unusually large blue-green algae blooms that have formed in waterways across California and the United States this summer. In California, water quality officials say the frequency and size of the blooms offer another sign that the state’s drought never went away, despite the near average precipitation that soaked the north state earlier this year.
The warnings span the state. Since July, officials have issued notices about potentially toxic blue-green algae in the Klamath River near the Oregon border; along an arm of the state’s largest reservoir, Shasta Lake; and at Pyramid Lake in Los Angeles County. They’ve attributed the deaths of thousands of fish along a section of Clear Lake to toxic blooms. Blue-green algae also has formed in parts of the Sacramento-San Joaquin Delta, prompting health warnings about green, malodorous water in Discovery Bay and Stockton.
“It’s fair to say that it’s looking like this year is not normal,” said Greg Gearheart, a deputy director at the State Water Resources Control Board, which issues algae health alerts. He said his office is tracking more than 30 reports of toxic algae blooms already this summer. Last year, through October, there were about 25.
California isn’t the only state experiencing an unusually slimy summer. Florida has declared a state of emergency stemming from dangerous blooms of algae in Lake Okeechobee that are spreading to the state’s Treasure Coast. In Utah, dozens of people reported headaches, stomach problems and rashes because of an algae bloom that formed in Utah Lake.
Scientists say it’s typical for some amount of blue-green algae to bloom this time of year, but that sewage, fertilizer and other pollutants released from cities, farms and industrial sites have contributed to an increase in their size and numbers.
In California, there’s broad agreement the problem has been exacerbated by the prolonged drought. The hot summer weather, combined with unusually low water levels at reservoirs and languid, warm river flows are creating conditions perfect for these microscopic organisms called cyanobacteria. Blue-green algae prefer water that’s warm, stagnant and clear.
And the rains that hit the north state last winter may have contributed, as well, washing into the waterways large amounts of nutrients that had accumulated during four extremely dry years, said William Cochlan, a San Francisco State University scientist who studies aquatic microorganisms.
Anthony Chu, chief of the state Department of Water Resources’ environmental assessment branch, said the increase in blue-green algae advisories also may reflect increased awareness: Officials have become more likely to report a bloom, based in part on a draft set of guidelines developed in recent years.
“We’re observing it, and we’re more aware of it,” he said. “But I think there also are environmental factors going on here.”
For people living near waterways under advisory, the message from health officials is fairly simple: When plumes of the bright, green algae are present, stay out of the water. Not all blue-green algae is toxic – but it can be, so caution is advised.
Ingesting toxic algae can cause severe stomach illness, and contact with skin can trigger rashes and other problems. Anglers are advised to avoid eating fish and shellfish caught in algae-fouled water.
Dogs and livestock are particularly at risk. They can die if they lap up water containing toxic algae or if they lick their fur after a swim.
At San Luis Reservoir, algae blooms form most every summer, but the lake’s low waterline has made this year’s bloom especially intrusive.
On the day Weber and Lewis were fishing, the reservoir was at just 10 percent of capacity, its lowest level since 1989. The lake normally refills with water pumped from the Sacramento-San Joaquin Delta, but pumping has been restricted this year to protect endangered fish.
The receding waterline eventually put the green gunk right above the intakes that siphon lake water to the treatment system for the Santa Clara Valley Water District, which serves nearly 2 million people in the South Bay. The district also has been battling algae issues from its water sources in the Delta.
While treatment makes the water safe to drink, the current method doesn’t eliminate the muddy smell and taste the algae leaves. The district said it was due to geosmin, a harmless compound produced by the algae. In June, the district began getting complaints from residents in San Jose, Mountain View, Cupertino and other cities.
To improve the taste and smell, the district is mixing in more water from other sources. That’s led to plummeting water levels at Coyote and Anderson reservoirs, popular summer recreation spots. Coyote closed to boating weeks earlier than normal because the water fell so low, and the water district is warning boaters that Anderson may soon close.
Shane Hunt, a spokesman for the U.S. Bureau of Reclamation which co-manages operations at San Luis Reservoir, said the good news is that the reservoir has hit its low point for the summer, and water levels are once more on the rise.
Elsewhere, relief from the green sludge will have to wait for the cooler temperatures and rainfall of autumn. At the Stockton Marina on Tuesday, the water was bright green, and the swampy odor of decaying algae hung heavy in the summer heat.
“It does smell rather bad. It does,” said Donna Walker, pausing from her afternoon stroll. “I wish we had some more water flow to kind of sweep it out a bit. But it is what it is. We’re in a drought season.”
Phillip Reese contributed to this report.