Cyanobacteria: Lake Toxin Poisons the Sea

By Jasjeet Dhanota

When sea otters with bright yellow gums started turning up on beaches in California’s Monterey Bay, Dr. Melissa Miller took notice. The first of these otters showed up 2007, and by year’s end 11 more were found dead with similar conditions.

“As we started doing the post-mortem examinations on some of these otters, we could see that the livers were very swollen and had areas of hemorrhage,” said Dr. Miller, a veterinarian and wildlife pathologist for the California Department of Fish and Wildlife Marine Wildlife Veterinary Care and Research Center. “In some cases, even if the animal had just died, we would lift the liver out of the abdomen to take a closer look and it would literally fall apart in our hands.”

After extensive testing, Dr. Miller, an affiliated faculty member of the Karen C. Drayer Wildlife Health Center at UC Davis, and her team determined that the culprit behind the yellow sea otters was a total head-scratcher — microcystin, a toxin produced by the freshwater cyanobacteria Microcystis, which is also commonly referred to as blue-green algae.

Sea otters live in the salt water of the Monterey Bay, so how could they be ingesting a deadly freshwater toxin?

Just over five miles inland from the Monterey Bay, Pinto Lake in Watsonville has been experiencing a series of wicked cyanobacteria blooms that leave the lake’s waters slimy and green.

Aside from the blooms, Pinto Lake is a treasure. It’s one of just four natural lakes in the Monterey Bay region, and it attracts a variety of waterfowl each year. Robert Ketley, a water quality program manager for the City of Watsonville, describes it as “drop-dead gorgeous.”

Yet, due to a series of manmade changes to the watershed starting in the 1850s, the Pinto Lake ecosystem has grown unstable over the years. Deforestation of the surrounding redwoods and local development have caused the water level to rise and nutrient-rich sediments to enter the lake. Meanwhile, agricultural practices have increased the fertilizer runoff into the water. As a result, the lake’s natural balance has shifted, causing large cyanobacteria blooms to begin in the 1970s.


Pinto Lake flows into Corralitos Creek, which then connects with the Pajaro River. The Pajaro River empties into Monterey Bay, creating a connection between the freshwater cyanobacteria blooms and marine wildlife. The result: yellow otters with failed livers.

It’s important to note, however, that Pinto Lake is not the sole perpetrator of cyanotoxins into the seas.

“I never want people to think that all of the otters died because of Pinto Lake,” said Dr. Miller. “Because that’s absolutely not true.”

The issue of cyanobacteria is widespread along the California coast and around the world. Recent studies have found it in the San Francisco Bay and at the mouth of the Klamath River.  In cities like Toledo, Ohio and Wuxi, Jiangsu Province, China, severe Microcystis blooms led to local drinking water crises.

“While Pinto Lake is a particularly relevant example, we see cyanobacterial blooms and toxins in every state and nearly every water body, from seasonal wetlands in California to Lake Erie,” said Dr. Raphael Kudela, a professor of Ocean Sciences at the University of California, Santa Cruz. “It truly is a problem that is in everyone’s back yard.”

Dr. Miller, however, was able to specifically link the toxins she was finding to the blooms at Pinto Lake, so she reached out to Ketley and the two have been working closely ever since.

“Individually, we could have gone on and done our various things,” said Ketley. “But it’s only by getting together, telling our stories together, finding our connections, that this has become so much more.”

Every fall, Pinto Lake's microcystin levels spike way beyond what's considered dangerous for humans and animals.

Today, the blooms continue to pose a significant health risk for people and animals in the area.

“In mammals, including humans, chronic exposure can lead to increased risk of cancer, while acute exposure can give you jaundice-like conditions, and at high enough concentrations can cause death,” said Dr. Kudela. “We can be exposed to the toxins through drinking water, consumption of algae, and even through breathing in toxins that become aerosolized.”

News stories of dogs dying from the toxin are not uncommon throughout the U.S. Dogs that swim in a body of water are often inclined to drink it without regard for the dangerous bacteria. Immediate treatment is vital, because there is no antidote for the toxins.

Fortunately, Cyanobacteria can be managed. Treatments have been proposed to trap excess phosphorous in the lake, and correcting this nutrient imbalance will reduce the amount of bacteria that grows there. In the long-term, the goal is to reduce agricultural runoff and improve watershed management to prevent future cyanobacteria superblooms. Small cyanobacterial blooms should always be expected, but it is possible to reduce the magnitude.

A solution may also arrive in the form of the Safe Water and Wildlife Protection Act of 2016 (AB300), which is a bill proposed in the state of California. If passed, it would create a centralized, comprehensive task force to respond to cyanobacteria blooms throughout California, including Pinto Lake.  

Meanwhile, veterinarians, community members, local government and growers are taking an interest in the issue and doing what they can, whether that is spreading the word, continuing their research or changing behaviors.

“Each and every one of them has a critical role to play and things they can bring to the table,” said Ketley. “Expertise, resources—everybody is valuable.”

The effects of cyanobacteria blooms are widespread, so managing the problem requires collaboration between many different fields. Human activities on the mainland trickle down to the ocean, impacting the health of wildlife and the environment.

“It’s a classic One Health problem,” said Dr. Miller. “We have to get together as a group and figure out what to do for the long-term.”


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