The Lumberjack student newspaper
Photo by Griffin Mancuso. The tide rising at Luffenholtz Beach.

Water hazards in Humboldt County 

Rough waves, rip currents, tsunamis, and toxic algae

by Griffin Mancuso

One of the perks of living in Humboldt County is access to the lush, sprawling redwoods and the coast, both of which are teeming with wildlife and great photo opportunities. With multiple beaches and rivers nearby, it may be tempting to brave the chilly waters with friends. If this is something you are interested in, do so at your own risk.


The most prominent risks you will face in Humboldt’s waters are the blue-green algae in lakes and rivers, and rough currents and sneaker waves in the ocean. Blue-green algae, also known as cyanobacteria, is something to watch out for during warmer weather in Humboldt. Its growth is fostered by nitrogen or phosphorus, which can be spread by runoff from cities during rainstorms. It can turn the water into a variety of colors and is more likely to bloom in slow-moving or still water at warmer temperatures, but it can also grow in the ocean with the right conditions. 

It can also be incredibly toxic to you and your pets if ingested. The Associate Dean of Marine Operations at Cal Poly Humboldt, Rick Zechman, says that even eating clams, oysters or mussels that have ingested toxic blue-green algae can have serious consequences.

“If you eat something that’s been concentrating Alexandrium or another toxic [genus of algae], your tongue starts to go numb, and your throat can become somewhat paralyzed, and it can cause you to stop breathing,” Zechman said. “ It can make you really sick, like vomiting and diarrhea. It can cause short-term memory loss. That’s where this idea of amnesic shellfish poisoning comes from.” 

While blue-green algae isn’t always toxic, there is no way to identify when it is or isn’t. Stay away from the water if it has a bad smell, is discolored, has green foam or mats on the surface, or there are many dead fish or animals nearby.


While Humboldt’s beaches offer plenty to explore, it is critical to keep a close eye on the waves. Sneaker waves, which appear suddenly and move very fast, are only seen in Northern California, Canada and Australia. Bridget Nichols, the Associate Director for Campus Recreation, emphasizes the importance of having awareness of your surroundings at the beach.

“If people aren’t keeping their eye on the ocean, they don’t really know the power and the impact,” Nichols said. “Trying to run away from a sneaker wave on a really steep beach – such as a place where you might go agate hunting or something like that – it’s going to be very different than at Moonstone Beach, where it’s a flat beach and you’re able to move a lot quicker through the sand.”

Photo by Griffin Mancuso. A sign warning visitors of the risks they face by standing on the jetty at the Samoa Dunes Recreation Area.

Tamara Barriquand, an assistant professor in oceanography and physics, explains the science behind sneaker waves and why they are more of a concern at steeper beaches.

“As a wave is coming into shore, it behaves as what we call a deep water wave. And then as it gets below, half the wave, like the depth… it’s now a transitional wave that’s starting to feel the bottom,” Barriquad said. “And so if that gets really shallow, really fast, all that energy is getting pushed up into the wave. And so you can get this wave that can get generated very, very big very, very quickly.” 

Sneaker waves are strong enough to knock you over and pull you into the ocean. These can occur no matter how calm the ocean appears.


The immediate concerns while swimming are the cold temperatures and rip currents. When the body is suddenly submerged in cold water, it can go into cold shock, which causes temporary muscle paralysis. Nichols strongly recommends wearing a life jacket when going kayaking or rafting in rivers. 

“When you first fall in the water your immediate reaction is to do a big inhale of breath and if you’re underwater, you can easily choke. So [the life jacket] is buying you time to get over and cough… it’s buying you time to orient yourself to your boat and get back to it. And if you can’t get back inside of the boat, it’s buying you time when your muscles stop working for a second.”

Grace Oliva, the Assistant Outdoor Program Coordinator and US Sailing Instructor for Center Activities, explains how rip currents are formed. 

“There will be a small divot in the beach right where the shoreline is, right where the water meets the sandy part. Over time, that can actually cause a deeper section in the beach… So when the water comes up on the beach from a wave, water always likes to go the path of least resistance and if it can go faster [or] farther, it will.”

Thankfully, it is possible to identify rip currents from the beach. Barriquand describes the visual signs to look out for, including white foamy water that builds up and is pulled out beyond the breaking waves, resulting in a noticeable difference in coloration between sections of water.

“The other thing you’ll see is right where the rip current is going, there won’t be any waves breaking in that location,” Barriquand said.

Rip currents are often dangerous not because of their strength, but because swimmers don’t know what to do in a rip current. If you find yourself caught in a rip current, Gracie Oliva strongly discourages students from trying to escape or swim against it.

 “You kind of just ride it like a lazy river,” Oliva said. “And then once you’re out of it, you’ll feel it. You’ll pretty much stop moving as much and then you can swim parallel to shore, and then you can swim into shore.”

If your friend or pet is caught in a rip current, attempting to rescue them can also put you in danger.


The least common but most dangerous beach hazard is tsunamis. While living in earthquake country puts Humboldt at a higher risk of experiencing tsunamis, they can sometimes be caused by other events, including landslides and storms. While tsunamis can travel from far across the ocean, they are easier to spot as they approach the shore. 

“If the water got really, really low really, really fast, then you’re seeing the trough of the tsunami,” Barriquand said. “And behind that is going to be a big wall of water.” 

If you notice these signs at the beach, head to high ground immediately.

When planning a trip to the beach, take the tide into account to prevent yourself from getting stranded, and read the surf report if you plan on going swimming. Be aware of cliffs and sudden drops while hiking near the beach and never turn your back on the waves once you’re on the shore. 

If you are traveling somewhere with no reception, tell someone where you will be. In the water, a wetsuit or life jacket is recommended even for experienced swimmers. Most beaches in Humboldt will have blue signs detailing the potential hazards there and how to handle them. In the rare case of a tsunami, learn your local evacuation routes.

BloomWatch App for reporting toxic algal blooms:

NOAA Coastal Hazards Resources:

SurfLine for daily surf reports:

California Tsunami Preparedness Guide:

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