Sweetwater Authority, already draining extra water supply, looks for more to combat algal bloom

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Facing its largest seasonal algal bloom in 20 years, the Sweetwater Authority may need to buy water to address the problem.

At its May 28 board meeting, the South Bay agency agreed to increase its budget for the year in case it must purchase more water to dilute the water supply. The agency says doing so would help mitigate changes to the water’s taste and odor caused by the algae.

With the new budget approved, the agency will gauge whether it will need to go through with the purchase, said Justin Brazil, the authority’s water quality director.

“We hope we don’t need to but we got to a point where we were getting pretty, pretty close to the bottom of that water budget,” he said. “We just want to make sure we have it there if we need to continue mitigating for algae blooms for the remainder of the fiscal year.”

Any water purchase would be minimal and would not affect the agency’s water customers’ bills.

For the past six months Sweetwater has been grappling with a number of pollutants in its main reservoir and has been using its water surplus to dilute the problem. Earlier this year, the authority transferred water to the Sweetwater Reservoir from Loveland Reservoir to lower levels of chemicals, known as PFAS, detected in the water. 

Now, in what they say is a separate issue, the agency would either use purchased water to dilute the algal bloom, or may also sell the purchased water to customers rather than diluting its own.

Though algal blooms are naturally occurring, the agency says, this year’s bloom has produced high levels of geosmin, the compound that produces musty odors in water. At the levels detected in the reservoir, the compound is non-toxic to humans, but Brazil said customers would be able to detect the “unpleasant” and “grassy” smell.

Algal blooms in reservoirs have become increasingly common in recent decades. One estimate suggests that mitigating blooms in the U.S. from 2010-20 cost more than $1 billion. Scientists link the growth to an increase of nutrients in the water as well as a warming climate. Runoff from expanding cities contributes to the problem.

The Sweetwater Reservoir is an eutrophic reservoir, a body of water with a high nutrient content. But as seasons and water temperatures change, the nutrients move and mix into the water creating conditions more favorable for a bloom.

That is one reason why the authority is also in the process of investing $3.3 million in a system that would aerate the water and keep the nutrients at the bottom of the lake in order to mitigate algal blooms.

That way, Brazil explained, “you constantly have a uniform water quality all the way from the surface to the bottom.”

Researchers say draining lakes can transfer nutrients and also promote algal blooms downstream.

Brazil says the agency does not test Loveland Reservoir in the same way it tests Sweetwater, but he knows that while the upstream lake is less impacted by urban nutrients, it still has had algal blooms. Transferring that water from the lake would introduce more nutrients like phosphorus and nitrogen into Sweetwater Reservoir that can worsen the bloom.

“It’s unavoidable that to some extent we’re gonna also capture nutrients from the watershed,” Brazil said.

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