Red tide is a common name for a phenomenon more correctly known as an algal bloom, an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water. It is usually found in coastal areas.
These algae, more specifically phytoplankton, are single-celled protists, plant-like organisms that can form dense, visible patches near the water’s surface. Certain species of phytoplankton, such as Dinoflagelate, contain photosynthetic pigments that vary in color from green to brown to red.
When the algae are present in high concentrations, the water appears to be discolored or murky, varying in color from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discoloration, and not all discolored waters associated with algal blooms are red. Additionally, red tides are not typically associated with tidal movement of water, hence the preference among scientists to use the term algal bloom.

A “red tide” off the coast of La Jolla, San Diego, California.
Red tide is a high concentration of Karenia brevis, a microscopic marine algae that occurs naturally but normally in lower concentrations. In high concentrations, its toxin paralyzes the central nervous system of fish so they cannot breathe. Dead fish wash up on beaches. Dense concentrations appear as discolored water, often reddish in color. It is a natural phenomenon, but the exact cause or combination of factors that result in a red tide outbreak are unknown. Red tide causes economic harm and for this reason red tide outbreaks are carefully monitored.
Learn more form Wikipedia




I think they once used this to explain away the ‘river of blood’ (the Nile) in Exodus??
Hi travelrat,
When people see this, I’m sure they think of the Exodus, and yes it had be used to explain it, especially as the Red Tide kills all the fish etc, that happens to be caught in it.
Fascinating!
Hi roughwighting1,
It certainly is, just amazing how dangerous nature can be sometimes.
I never realized it was so crimson! Wow. These are amazing scenes.
Hi SDS,
It’s almost like a dye isn’t it. It’s amazing how an microscopic algae can change the color of the water.
I’ve not seen the water so red, but we certainly have to watch for Red Tide season each year on West Coast Canada. I’m heartsick about all those dead fish…
Hi souldipper,
The green algae also can be harmful to marine life if it is thick enough to cut off the oxygen in the water, it is truly sad to see what damage these algae can do.
What a shame… Sardines are an excellent source of Vitamin D and calcium. It’s sad to see so much evidence of how badly we’ve thrown Mother Earth off balance…
Hi Barbara,
The Algae really does a lot of damage to our Marine Life, it really is sad to see.
This creeps me out whenever I see it. Yes, I know it’s a natural phenomenon, but still…It reminds me of the rinse water after i used to color my hair (without the fish, of course). That’s why I went natural. Thanks for the pictures.
Hi Barb,
I agree, it just doesn’t look right, it has an eerie look to it I think.
I have never seen this weird phenomenon! I have heard of it . That is some cool information thanks for sharing. I feel sorry for all those marine animals
How often do they come in? My sister always talks about them living off the coast but I really never new what they were. Mother nature has a sick sense of humor!! Does it have to be RED?? LOL
Hi Peggy,
Yes it’s amazing what good old Mother Nature is capable of doing. I don’t know how often they occur, I don’t think there is any set timing on how often they occur, scientists are still working on how it all happens. The most frequent blooms are the red and green algae, when this occurs in small fishing areas you can imagine the damage it does.
Wow! I have heard of red tide but never seen it like this before. I lived in SoCal most of my life and didn’t know about San Diego either. Was this occurrence this recent? Very sad about Costa Rica too. So many populations do not understand what they are doing to their environment, and ultimately, themselves… the US included of course. ~ l
Hi pixilated2,
It is amazing to think an algae could do so much damage. These algae, the red and the green have been happening for millions of years, and it all occurs naturally. Unfortunately even though scientists know how the water discolours, they have not worked out a way of how this can be stopped.
Once the algae gets really thick it cuts the oxygen off and the marine animals can no longer survive. We can only hope that one day a solution is found that can stop this from happening.
Sorry, I should have mentioned that I was referring to the loss of Mangroves in CR and the deforestation as a cause of the pollution and the killing off of the fish. Hence my comments about what we are doing to our environment and ourselves. ~ L
I agree with you there. Mangroves really should be left, they are used by many species of marine life for breeding and feeding. Our mangroves here in Australia are protected now, and in some areas the mangroves are floushing.
Remarkable. We have red tide in the spring and early summer here at Cape Cod where I like to go when I’m not at Hill-Stead. You can’t eat the shellfish during that time. Later on, at the Cape Cod National Seashore up toward Wellfleet, we have nasty red seaweed we call “mung”. It sticks to your bathing suit and you can barely get it out. Lovely blog. I’ll keep coming back! Thank you.
Diane Tucker
Naturalist
Hill-Stead Museum
Farmington, CT (USA)
hillsteadblog.com
Hi Diane,
It does sound like a nasty seaweed, I have never heard of it before. Something that sticks to your bathing suit sounds awful.
Thank You very much for taking the time to comment, I have your blog in my RSS feed, so I will also be back to visit you as well.
Wow, those are some pretty alarming photos!
Hi Bruno,
They certainly are, nature has a way of just throwing these things at us every now and then.
and everyone wonders what the Univ of Alabama means when they call themselves the Crimson Tide…
sounds a little more menacing now!
Hi Vince,
It certainly does sound a lot more menacing. It is amazing the damage that this can do.
Thank You for taking the time to comment.
I know, I know, a person living in Wales couldn’t possibly compete with the exotic infestations you’ve shown us above,but…even Cardiff gets its fair share of green algae. I vaguely remember some professor saying on telly once that we should try and harness this algae-power for something or other, probably fuel, methinks. Thanks for sharing these remarkable pics. with us and your informative blog.
Hi mariathermann,
It would be very good, if the powers that be could find a use for this awful stuff.
it must have a good use – cancer cure or something – what dreadful stuff!
Hi Theresa,
Hopefull in the future they may discover something this algae is good for.
That’s unbelievable! For my first pics of the week feature, I had a photo of bioluminescent plankton (I think) of this sort, and it was like a blue glow they gave off….but the red is really tripped out!! Great post!
Hi Zen and Genki,
It’s is unbelievable, the things nature can to.
This is so worrying – it was dreadful to see all those dead fish. Did the red colour in the water and the fish remind anyone else of the Old Testament? Thank you for that, it was most interesting.
Hi loonyliterature,
I think it is one of things you first think about when you see this, is the Old Testament, so very, very similar.
I’m glad you found the post interesting.
Oh yes I did. I will be coming back for more.
Very informative! I also wanted to thank you for visiting my site ‘foreverpoetic.wordpress.cm
Hi Wendell,
I’m really glad you enjoyed the post.
I also enjoyed some of your posts as well, and have you in my RSS feed.
Thanks for visiting my site! Have a wonderful weekend!
Hi Wendell,
You are more than welcome.
Thank You very much for doing the same.
I grew up in San Diego, and remember hearing news announcements, “Don’t eat shellfish, it’s red tide,” throughout my childhood (the ’60′s). But I have never seen it myself. Those aerial shots are terrific. It really does look like blood, doesn’t it? Interesting fact I learned from your post – that sometimes the phenomena isn’t dense enough to cause the coloration to be visable, but it can still do the damage.
Hi Donna,
It certainly does look like the water is covered in blood, toxic and dangerous as well to the sea life. Truly nature at it’s worse, for all marine life.
Mag’s thanks for visiting my site today!!! “Hugs”!
Hi Wendall,
The pleasure was all mine, I enjoy your posts.
Thank you so much for these pictures & this most informative post…
Hi Lindy Lee,
I’m glad you found the post interesting.
Reblogged this on shooken.
I’ve heard of this phenomenon from my parents. This is the reason why we’ve taken off mussels from our diet. I heard eating the mussels when there was red tide killed a lot of people in the Philippines.
Greetings from California.
Hi renxkyoko,
I hadn’t heard about the mussels, that is terrible. These type of tides are just so dangerous.
Very interesting. Had heard of it, but didn’t know a thing about it! Thanks for posting!
Hi allthingsboys,
Nature can be dangerous at times, just amazing how toxic this is.
It’s amazing how something so beautiful and so spectacularly looking can be so deadly…
Hi nyparrot,
It does look spectacular, the power of nature is always amazing and in this case deadly.
Hi,Mags,
Thanks for making people aware of terrible acts of nature like RED TIDE. We have been watching stories of coral reefs being destroyed and fish dying from this natural source around the world. You have one of the most interesting and informative blogs I have the pleasure of reading.
Hi Ronnie,
It is definitely one of Natures dangerous things, so deadly to all marine life unfortunately.
Thank You for your very kind words.
Excellent work again Mags ,Happy weekend
Hi Jake,
Thank You.
You have a good weekend as well.
Very informative indeed. On the Muscat coastline ( where I live), we also see this fluorescence tide. Am told that is also due to Algae but not sure.
Cheers
Shakti
Hi Shakti Ghosal,
It must be unreal to see this happening in front of you, it is just so deadly to marine life, yes it is a form of Algae, very toxic.
Thank you very much for visiting and also for your comment.
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