Last summer’s harmful algae bloom that caused a massive fish kill throughout San Francisco Bay had a devastating impact on Lake Merritt. The microscopic plant responsible for the “red tide,” Heterosigma akashiwo, caused oxygen levels to plummet, leaving fish, mollusks, crustaceans, and other creatures unable to breathe. Their carcasses littered the lake’s shoreline for weeks and naturalists worried the die-off would ripple throughout the food web, starving mammals and birds.

But as the seasons changed, nature, as it so often does, began healing itself. Winter arrived, rain and tides flushed the lagoon, and life slowly reappeared.

Even so, the lake’s many stewards are deeply worried about its future.

Another algae bloom isn’t just possible, it’s almost assured. And this winter’s record series of storms has presented a new, surprising problem—too much freshwater gushing into the lake has reduced salinity levels, to an extent that could harm lifeforms adapted to brackish and saltwater environments.

“Now that we have red tide in the lake, it won’t go away. It goes dormant,” said Josiah Albertsen, a board member of the Lake Merritt Institute. “When the conditions are right—temperature, nutrients—it’ll come back. That means we could have another red tide this summer.”

Volunteers, the city, and technical experts are scrambling to do something before it’s too late. In the short term, they’re stepping up efforts to study the lake and better understand the problems. In the long run, they want to make investments that could restore a greater balance to Lake Merritt, ensuring its resilience against climate change, pollution, and other threats.

The Lake Merritt Institute, a nonprofit that educates residents and helps keep the lake’s waters clean, recently launched an ambitious fundraising campaign to pay for a pilot project and long-term solutions, including equipment that could improve water quality, potentially creating refugees inside the lagoon for when harmful algae blooms reappear.

James Robinson, the Lake Merritt Institute’s executive director, said the lake has reached a crisis point and it’s time for Oakland to act. “When dead fish and dead marine organisms show up, these are indicators that a body of water needs some help,” he said. “If we enjoy looking at fish or we enjoy boating on the lake, it’s important that we take care of the water.”

And it’s not just about wildlife. As Oakland’s most popular park, Lake Merritt sees thousands of visitors every week, playing host to festivals, markets, dance parties, music, skating, and more. All of this human activity depends on a healthy lake.

“It’s important for all of us as a community to make sure that we take care of it,” said Robinson.

An effort is currently underway to gather an unprecedented level of data about the lake ecosystem, data that can be used to design systems to improve water quality and respond to future crises. Lake Stewards are hopeful, but so far they’ve raised a small fraction of the funds needed for short-term work. There’s still a lot to learn about the lake ecosystem. And the funding they’ll need for permanent water quality systems that could stop a future fishkill has yet to be identified.

Watching the lake breathe in real-time

Lake Merritt Future
Eli Kersh of LakeTech steers toward a sensor buoy. Credit: Amir Aziz

Eli Kersh backs his truck up and eases his aluminum boat off a trailer into the lake on a recent Friday morning. He’s come out to check on three buoys he placed in the water, each outfitted with a chain of sensors that continuously monitor water quality.

After a short trip across the lake from the boathouse he pulls the first buoy up from near the entrance to the channel under E. 12th Street, where Lake Merritt connects to the Bay. The bowling ball-sized float is attached to a long tube that contains various sensors. Below is a line dangling into the water where another array of sensors is suspended just off the lake’s muddy bottom. The gadgets have been submerged for a month and they’re already covered in brown, slimy layers of algae.

“Lake Merritt is what we call highly productive,” says Kersh. Its waters are filled with nutrient runoff from Oakland’s streets that algae, bacteria, and other microorganisms feast on.

The buoy has been pushed from its original location, possibly by powerful recent storms. After scrubbing away scum, Kersh drops the chain of sensors back into the water. The top and bottom sensors are transmitting a constant flow of data from a tiny antenna atop the buoy to cellular towers. The data then goes into a system managed by Kersh’s company, LakeTech, and he and his customers—in this case, the city and Lake Merritt Institute—can pull up water quality charts in real-time.

Lake Merritt Future
One of LakeTech’s sensor buoys near the estuary channel. The buoys send data wirelessly that can be viewed on a cell phone. Credit: Amir Aziz

The second buoy near the tip of the lake’s western finger is missing its antenna, possibly yanked off by a curious bird or a mischievous person who snagged it while fishing. But it’s still transmitting its data, says Kersh. On his cell phone he glances at charts and maps revealing what’s happening in the lagoon.

The data include levels of dissolved oxygen at the top and bottom of the lake; surface and bottom temperatures; turbidity, or the cloudiness of the water due to suspended particles; chlorophyll levels which can show how much algae is present; and the different levels of salt in the water, from the surface to the bottom.

“What’s unique about lakes is they actually breathe,” said Kersh.

During the day, oxygen levels rise as plants like algae photosynthesize. At night, oxygen drops, and it can plummet during a red tide event to levels that cause mass fatality among fish and invertebrates. This is, more or less, what happened last summer when an algae bloom blanketed the Bay and drifted into Lake Merritt, according to water quality agencies and researchers.

Other complicated processes are constantly at work in the lake. Water temperatures fluctuate with the weather. Freshwater floats atop saltwater, sometimes creating strange layers in which warmer saltwater from the Bay sinks to the bottom of the lake with cold freshwater from creeks and storm drains hovering at the surface.

Lake Merritt Future
Eli Kersh scrubs algae, other aquatic plants, and critters from one of the sensors he’s placed in the lake. Credit: Amir Aziz

“There are complex dynamics taking place that we need to really understand so that we can design an oxygenation and aeration system that is suitable to insure that we don’t get another fish kill event in the future,” says Kersh.

Kersh is gathering all this data for the city and Lake Merritt Institute with the goal of helping create a blueprint for a system that will continue monitoring water quality and oxygenate the lake when it’s needed.

At the third buoy near the Pergola and Colonnade, Pelicans, seagulls, and cormorants are roosting on floats. Oxygen levels in this area are high, a good sign for fish and other aquatic creatures. But the winter weather has caused another shift in the lake’s dynamics that some are concerned about.

Drought-busting winter rains have reduced salt levels in the lake

Clams that died during last summer’s red tide. Mollusks are also susceptible to drops in salinity in the lake, especially bivalves which are stationary. Credit: Amir Aziz

Katie Noonan of Rotary Nature Center Friends walks along Lake Merritt’s shoreline almost every day to survey the wildlife: mussels, smelt, striped bass, ducks, bioluminescent worms, and the occasional Chinook salmon. 

She enjoys exploring biodiversity at the U.S.’s first official wildlife refuge—the lake was designated a refuge in 1870—partly because she’s reminded it’s more than just a recreational area. “Some of the organisms moderate pollutants” that drain into the lake, Noonan explains, cleaning the water on its way to the Bay. “Studying the lake helps increase our understanding of being a part of nature.”

Rotary Nature Center Friends works to protect wildlife at the lake. That’s why Noonan is concerned for its well-being after a series of atmospheric rivers pummeled the East Bay with strong winds and heavy rain.

“Every time there’s big rainfall, there’s a drop in the lake’s salinity level,” said Noonan, who has sampled and studied the lake’s water for many years. “And that’s a problem for many of the invertebrate species and some fish species because they depend on a certain amount of salinity in their bodies, otherwise they’ll take on water and won’t survive long.” Organisms like mussels and clams which can be found clinging to rocks are at high risk.

Sensors installed by LakeTech measured recent salinity levels in Lake Merritt. The green areas in the chart show recent days on which salinity dropped rapidly near the surface and halfway to the bottom of the lake in most areas, likely because of intense rain that increased freshwater levels. Credit: Image courtesy of LakeTech and Lake Merritt Institute

Lake Merritt is actually a tidal lagoon connected to the Bay which naturally flushes it with saltwater from the Pacific Ocean. This makes Oakland’s crown jewel the perfect ecosystem for marine life to prosper when conditions are ideal. But the red tide and excess freshwater have been a double whammy on the ecosystem.

Robinson of the Lake Merritt Institute is concerned that an oversaturation of freshwater could lead to freshwater resting directly on top of the saltwater through a process known as stratification. “The topwater can be highly oxygenated and the saltwater bottom layer could contain lower levels of oxygen, making it more difficult for marine life to breathe,” Robinson said.

Atmospheric rivers aren’t an unusual occurrence and the lake experiences a drop in salinity every wet season, said Noonan. Freshwater comes in from the 62 storm drains emptying directly into it, as well as rainfall directly above the lake. Lake Merritt’s tidal gates, which were put in place to prevent flooding, are managed by Alameda County. When they’re closed, they prevent saltier water from refreshing the lake and freshwater from draining into the Bay.

Part of the concern lies in how climate change might be accelerating the frequency and intensity of storms, and the conditions that cause red tides. “Climate change is right here,” said Noonan. “Sea level rise, weird weather. We’re forced to think about it more, which is something you can kind of sense at Lake Merritt where everyone [in Oakland] mingles together.” 

Fish Death at Lake Merritt 15
Pelicans lost a major source of food last year when anchovies and other small fish were killed off during the red tide. Credit: Amir Aziz

Noonan and other naturalists paid close attention to the lake’s recovery following last summer’s red tide. She tracked the reappearance of wildlife, especially fish and invertebrates. She was especially surprised to see nudibranchs, a type of sea slug, coming back. These colorful, soft-bodied mollusks are found throughout the world because they can adapt throughout the world. Biologists pay a lot of attention to these unique little creatures because their presence helps us understand how an ecosystem is doing. 

But the torrent of rain in January, February, and March may have dampened the recovery process. The nudibranchs haven’t been spotted in the lake recently due to low salinity levels and other species have left too. The impact of freshwater may have been less intense had the red tide not done so much damage already.

Circulation fountains and oxygenation devices

A worker lifts one of the city’s decorative fountains from the lake to repair it last year in hopes of restoring some oxygen to the lake. Credit: Harvey Castro

During last summer’s fish die-off, the city and Lake Merritt Institute rushed to try to fix the two fountains that adorn the lake, one at the tip of the western finger near Children’s Fairyland, and the other near the Pergola and Colonnade. The idea was that circulating water could replenish the lake with oxygen, helping some fish avoid suffocation.

But the existing fountains are decorative and aren’t effective at injecting oxygen into water, said Kersh. Not only are they bad at improving water quality, but they also consume lots of electricity and break down frequently, often getting clogged by weeds and algae. He said the city should invest in smaller propellor-style circulating fountains that will more effectively mix water from deep in the lake up to the surface and add some oxygen. Another system he says the city should consider using is oxygen saturation technology.

“They take oxygen gas from nearby on the shore and saturate the water and release it into the lake,” he said. “They’re more expensive than artificial circulation systems [fountains], but they’re foolproof.”

If installed in the right locations, the impact could be big. According to Kersh, the lake’s western finger is “hydrologically isolated” from the rest of the lake due to the rises and falls in the lake’s bottom topography. “It means if we put an oxygenation system here, it’ll hold that oxygen better,” he said, potentially creating an underwater cove where fish could take refuge during a red tide. The kind of technology available today, he added, can be set up so that oxygen pumps are triggered automatically when there’s a dangerous drop.

Similar equipment could be set up near the Pergola and Colonnade, or other locations around the lake. The data Kersh is gathering right now will inform whatever plans he, the city, and Lake Merritt Institute come up with.

Lasting solutions to improve water quality in Lake Merritt are estimated to cost a few million and would involve ongoing monitoring combined with new circulation and oxygenation systems. 

In the meantime, the data gathering Kersh is helping with will be used to set up some kind of pilot project that could demonstrate the effectiveness of these kinds of interventions.

The city didn’t respond to a request for an interview for this story. But Terri Fashing, Oakland’s watershed program supervisor, recently told members of the Measure DD Coalition, a volunteer board that helps oversee the spending of Measure DD bond funds, that her team “would like to stay focused on making sure we could get equipment into the lake this summer on some sort of pilot basis.”

Albertsen of the Lake Merritt Institute said one short-term and affordable goal could involve aerating fountains. “We’re looking at four additional fountains that would be shallow water operating and could create refuges near the beach, the turn toward the finger area,” he said. “If this is going to happen again, possibly by June, we need places where fish can go where there are oxygen safety zones.”

To pay for these, the institute launched a GoFundMe campaign one month ago with the goal of raising $150,000. According to Albertsen, $18,000 would allow the institute to purchase four new shallow-water aerators. An additional $20,000 could pay for a fourth water quality monitoring buoy, one that can measure levels of nutrients, which are a key factor in causing harmful algae blooms. The institute is also hoping to raise enough money to hire additional staff, repair its trash collection boxes, and replenish other equipment.

So far, they’ve raised just over $8,000, the majority from small donations by Oakland residents.

Lake stewards say it’s a struggle against the clock. “All of the preconditions for what happened last summer are going to be in place this coming summer,” said John Bowers, a board member of the Lake Merritt Institute and member of the Measure DD Coalition. “There’s not a lot of time between now and when those conditions will be in place again. That’s a frightening prospect.”

Another possible source of money for the pilot project or long-term investment is Measure Q, a 2020 voter-approved parcel tax, 64% of which is used to pay for park maintenance, and 5% specifically for water quality projects. Fashing told the Measure DD Coalition at their meeting on March 20 that her team is looking into accessing some of these funds.

However it’s paid for, lake advocates feel confident they’re on the right path.

“Once we show in the pilot project area that dissolved oxygen levels can support the biological resources of the lake, then we can make the case that we need a lakewide oxygenation system to extend that positive effect,” said Bowers.

Kersh, who grew up in Oakland and lived for a time right next to the lake, said he’s looking forward to helping the city and Lake Merritt Institute design the pilot project.

“It was unfortunate that it took a red tide for everyone to rally and finally get on the same page and start getting resources together and studying it,” he said.

Robinson agreed. “It’s a sad event that happened with the red tide and fish kill,” he said. “But we can also use that as a lesson to point to and say, ‘Hey city officials, you don’t want this happening at the jewel of Oakland again.’”

Ricky Rodas is a member of the 2020 graduating class of the UC Berkeley Graduate School of Journalism. Before joining The Oaklandside, he spent two years reporting on immigrant communities in the Bay Area as a reporter for the local news sites Oakland North, Mission Local, and Richmond Confidential. Rodas, who is Salvadoran American and bilingual, is on The Oaklandside team through a partnership with Report for America, a national service program that places journalists into local newsrooms to report on under-covered issues and communities.

Before joining The Oaklandside as News Editor, Darwin BondGraham was a freelance investigative reporter covering police and prosecutorial misconduct. He has reported on gun violence for The Guardian and was a staff writer for the East Bay Express. He holds a doctorate in sociology from UC Santa Barbara and was the co-recipient of the George Polk Award for local reporting in 2017. He is also the co-author of The Riders Come Out at Night, a book examining the Oakland Police Department's history of corruption and reform.