Answers needed quickly as decomposing algae turns sea red

Photo: Sanidad.

Updated 25 September: The microalgae has been widely acknowledged as “not harmful” except in prolonged massive exposure or for those with a skin sensitivity, but a new development is less benign. It has been noted globally that as these blooms decay – and they have been seen as far afield as Hawaii, California, Mexico – the decomposition process turns the browny foam red, causing a phenomenon known as a Red Tide. Unfortunately, some Red Tides are toxic even though the original bloom which caused them is not. Even more unfortunately, the sea in parts of the Santiago del Teide coastline has turned red after suffering an algae bloom.

Tenerife needs answers quickly. What is the latest on what is being done about the algae blooms? Is the red sea along the Santiago del Teide litoral actually a Red Tide? If so, is it of the sort that is toxic? What can be done, and what is being done, to try to get the blooms out to sea so that our bays and beaches don’t look like slaughter coves?!

Updated 17 August: In an extraordinary press conference yesterday, two government departments came together to issue a statement on the microalgae around Canarian coastlines. Despite the argument over what part untreated sewage plays in the frequency and extent of the blooms, the Consejerías of Sanidad and of Política Territorial, Sostenibilidad y Seguridad say that after many studies, and with the collaboration of many independent scientists, they can jointly advise the public that the blooms are a natural cyanobacteriological phenomenon which is intrinsically harmless, even if some people might have a particular sensitivity which produces a minor skin reaction, for which reason bathing is not advised where blooms are visible.

The two departments also say that the public is going to have to get used to these outbreaks because the blooms are here to stay since they are a product of warming seas. And so, even if the untreated waste problem were solved tomorrow, we would still have the algae. Director General of Public Health, José Juan Alemán, and Director of Nature Protection, Susa Armas, said that the departments have been collaborating closely for the last couple of months, and seeking advice and opinion from experts like Dr. Emilio Soler, taxonomist and researcher of the Spanish Algae Bank; Rogelio Herrera, Dept of Environment Biodiversity technician and doctor in Sea Sciences; María Luisa Pita, Chief of Environmental Health Service; and Esther Fierro, responsible for beaches.

José Juan Alemán said that more than 50 days have passed since the beginning of this episode, and the Government has been informing the public throughout the period, both via the media and through social media channels and consultation services such as the official healthcare website The director of Public Health stressed that skin problem statistics were little different this year from any other, and as to the acknowledged increase in numbers of cases of Hepatitis A, he said that direct transmission, person-to-person, via fecal-oral, through dirty hands and close physical contact with an infected person, remains the most frequent mode of transmission of hepatitis A in our environment, and so the Government recognized it must reinforce the message through education on hygiene and sexual behaviour. The current outbreak of Hepatitis A, he said, is also affecting other regions in Spain as well as other European countries, and was detected in the Canary Islands in January 2017, and is unrelated to the blooms.

Finally, he reiterated that the current scientific evidence has been established by the community of experts in the field, and that it categorically disassociates the development of microalgae bloom with untreated sewage discharges. He referred to the regular testing of sea waters showing that the sanitary quality of the beaches of the Canary Islands is excellent, a verifiable fact additionally borne out by the numbers of blue flag beaches in the islands.

The Government says that the General Directorate of Public Health has been responsible for the Health Surveillance of the Quality of Bathing Waters for more than 30 years, and follows criteria set by the World Health Organization and European and Spanish regulations. There is a census of 175 beaches with 217 sample points in the Canaries which are inspected and analysed for, among others, fecal contamination indicators such as E. Coli and intestinal Enterococcus. These samples are taken every two weeks or monthly, depending on the time of year, attendance and any anomalous results. This is all organized nationally by the NAYADE system, and the results of the inspections and analyses are notified to Sanidad, and are available to the public HERE (there is more information HERE on how to use the site).

The Government’s clear line here is that the the data are irrefutable, and the European Commission itself confirms that the Canary Islands’ bathing waters meet the highest quality standards set out in the Directive. It does not alter the fact, however, that the EU is also critical of Spain generally for untreated sewage being pumped into the sea and something will have to change if the EU is to be satisfied in this respect. It was no doubt in connection with this that the Director General of Nature Protection, Susa Armas, reported that the last census of discharges into the sea was in 2009, and that a new one is currently being finalized: it will be published in November.

Updated 31 July: The Canarian Government’s Health Department has spoken out against the “many hoaxes” circulating on social media about the microalgae around the islands’ coasts over recent weeks. Sanidad says explicitly that “these concentrations of microalgae have absolutely no relation with spills of sewage”. The Health Dept calls on the public to inform itself well before helping contribute to fake news, and repeats Professor Sansón’s advice (update immediately below) that the algae are cyanobacteria, specifically Trichodesmium Erythraeum, also known as sea sawdust.

Sanidad says that far from social media claims that the blooms are caused by the algae “feeding on sewage”, they actually appear in Canarian waters in  high temperatures when there is also a lack of activity in the marine currents or prolonged periods of calima. The algae reproduce and disperse quickly but their colour, added to the smell of dying algae, makes the confusion understandable, says the Health Department, but confirmed scientific analysis has demonstrated the cause is not sewage leaks.

The official health advice about bathing in affected beaches is that it is advisable to avoid them because although most microalgae are harmless, some can produce toxins with different health effects, either by contact, by the intake of water containing them, or by the inhalation of the aerosols caused by the waves. The concern, however, is of a reaction to algae, not sewage, nor e-coli, an entirely separate matter which is dealt with by regular routine testings.

Updated 29 July: The Canarian Meteorological Association says that climate change could be the reason for increasing instances of algae blooms around the entire Canarian coast. Referring to statements by Marta Sansón, Marine Botany professor at La Laguna University, ACANMET clarifies that these algae are cyanobacteria, which are generally tropical, and a 2º rise in sea temperatures is sufficient to cause an increase in blooms in colder waters. This is exactly the amount by which the temperature of the seas around the Canaries has risen over the past thirty years, as confirmed by several studies carried out by the university in Las Palmas.

These blooms occur in conditions of calima which can bring not only calmer and warmer waters, but also air that contains what the Professor calls the “essential nutrients” on which the bacteria thrive, like iron. She pooh-poohed the idea that the cause was sewage spills, even though it is a reason with a massive hold on social media: spills have always been an issue at various points around the islands, she said, but we have not previously had this number of blooms, nor in such a generalized way.

Updated 26 July: Tenerife president Carlos Alonso has issued a statement insisting that the appearance of microalgae around the island’s coasts is unconnected with any problems of “spills”.  President Alonso said that the appearance of patches around the coastline is due to climatic conditions, and is being monitored by individual municipalities and the Canarian Government. The Cabildo is meanwhile investing in sewage and water treatment infrastructure to ensure Tenerife’s coastline was kept clean, an investment that amounts to near €50m over the next three years. The president repeated the advice given by the Canarian Government’s Public Health Department to avoid bathing or direct contact with water where an oily and foamy bloom appears.

Updated 24 July: Guía de Isora Ayuntamiento has announced that since the analysis results are good, and since the microalgae has moved away from the coast, the council is opening Playa San Juan and Abama beaches again. The council repeats the official stance that it is a natural phenomenon and represents no risk to health except in those with some type of allergy or particular skin sensitivity.

Updated 22 July: Guía de Isora Ayuntamiento says that the specific analysis carried out at Playa San Juan confirms that it is microalgae carried by flow from other parts of south Tenerife, and that there is no indication of any spillage of fuel or other type of residue. The council says, however, that it still advises the public not to bathe in the water at Abama and Playa San Juan beaches because the microalgae is still present. The council hopes that the normal sea currents will disperse the algae in the next few days. 

Updated 2pm: Guía de Isora Ayuntamiento has raised the red flag to ban bathing at Playa de San Juan due to the appearance of the algae. The council says that in addition to routine water testing which was carried out first thing this morning, a second more specific analysis has now taken place. The council’s environment department does not believe that the algae represents a danger but is acting in accordance with the advice from the Canarian Government’s Health Department. More will follow when they have the results of the second analysis, it appears.

Updated 12.30pm: In addition to the official advice and information from Sanidad this morning, Adeje Ayuntamiento has issued the following statement about the matter:

The Adeje department for the protection of health, following recommendations issued by the regional department of public health, is advising the public to avoid bathing in the sea where micro
​-​algae blooms have appeared in swimming areas of Adeje. Physical contact with the blooms of micro​-​algae, both in the sea and on shore, should also be avoided.

The health department, in co-ordination with the department with responsibility for beaches, has detected the presence of the algae, which appears on the sea surface. The colour is similar to light brown sand, and has been seen along various parts of the island coast line in recent days. These ‘blooms’ of microalgae, which have been seen in bathing zones, have not actually caused any notable damage to date.

Photo: Adeje Ayuntamiento

Furthermore, the local health department is stating that this is a natural phenomenon produced under certain environmental conditions, the consequence of diverse biological factors, climatic and environmental. The blooms appear sporadically and the vast majority of microalgae are innocuous, although some may product toxins that could affect health, in particular via direct contact, ingestion of water with spores, or inhalation of sea spray.

This council, as a general recommendation, is passing on the advice of the regional department of health, not to bathe in the sea and avoid direct contact with the algae in bathing areas where ‘a change in the colour of the sea water is detected, with spots of intense colour variation, where there is minimum transparency’. If there are beach activities scheduled, the organisers should take these precautions into consideration, and follow the advice at all times of the lifeguards and local police on duty.

The councillor with responsibility for health, Amada Trujillo Bencomo, has been in contact with the Adeje health centre and to date there have been no reported incidences of anyone presenting with injuries or conditions related to the algae.

Department of Communications

Updated 21 July: With the recent heatwave, the microalgae problem has returned, with all parts of Tenerife finding discoloured foamy patches off the coast. As last month, Sanidad advises bathers to avoid the water at beaches where a “massive floration” – a “bloom” – has come into land, and councils have been asked to put up signs or advice notices for beach users where the algae has been detected.

Sanidad has again confirmed that these blooms are a natural phenomenon produced by diverse biological factors, environmental and climatological, the majority of which are harmless. Some, however, can occasionally produce toxins that affect health, whether by skin reaction on contact, digestive if swallowed, or even if spores are inhaled from sea spray.

The basic message is as before, that there is a possible remote danger if, and only if, the blooms move close to the coast but while out at sea, there is no suggestion that councils should restrict bathing. Given that the above picture shows what the sea looks like when blooms approach beaches, most people would probably choose not to go in the water anyway.

Original post 27 June: The Canarian Government’s Public Health Department has advised Ayuntamientos that they might find coloured marks on the sea in their areas because of an increase of algae. Although this was purely for the councils’ own information, public concern has been generated by some releasing the notice. The Government has confirmed that this is a natural phenomenon which intrinsically causes no health danger, and there is no suggestion that councils should restrict bathing, though they have been advised to close beaches as they might feel appropriate if the problem moves closer to the coast.

To be explicit, this is a separate issue to the E.Coli problem which is specifically affecting the coastline from Candelaria to El Médano, and is still under investigation. The algae which is the issue here can cause skin and gastric conditions but only where there is a “massive floration” causing major discoloration and foamy water, under which circumstances most people would probably choose not to go in the water anyway. This is why the councils were advised by the Public Health department so that they could close beaches where it became obvious through discoloration and foam that there was an issue.

The Government confirms that in normal quantities, the algae is harmless, and given the Government advice and the councils’ powers to close beaches affected, by definition any beaches that remain open are safe. Sanidad has anyway linked the phenomenon with the weekend’s heatwave and says that the algae is now dissipating.


  1. The Canarian sewage systems were designed to allow the automatic release of sewage at high tide. The ebb tide would then take the the treated sewage out to sea. It appears to me that the quantity of sewage is perhaps more than the treatment plants’ capacity. Perhaps some of the sewage has not been completely treated. A good system that is being asked to do too much? Benidorm is in the Meditteranean. They do not have the luxury of the high Atlantic tides to clear the sewage. I have been on holidays to Mallorca, Menorca, Zante, Corfu, Rhodes, Crete and Kos. Have never seen the like of the sewage slicks you see at El Medano . Costa Adeje to Los Gigantes. Perhaps ask mainland Spain just how they do it

  2. Currently in Benidorm which is hotter but the seas are very clear and algae free – think they deal with sewage correctly! Canary islands need to invest in the basics ( sewage disposal) before 200 million pound New Ports, beaches, racing tracts etc. So so clean Benidorm.

  3. This is a very interesting article about the coastal pollution of Canarian waters, in a journal which promotes social justice and accountability on the islands. It accuses the government of failing to treat sewage properly. You can read it HERE. Use Google Translate to make it English.

  4. On scientifically renowned US web pages, you can clearly read that there is indeed a link between algae explosion and dumped waste water.
    When wastewater spills or is dumped into a body of water, it contains pharmaceuticals, synthetic hormones, pollutants and nutrients that can feed algal growth.
    Canarian Government’s Health Department has to consult the studies of their American colleagues.

    Google search

  5. Sorry Janet missed that you had already posted a link to the same site!

  6. I used to holiday on the Gulf Coast in Florida and your article has reminded me that every so often the locals sunbathing on the beach would cry out “red tide, red tide” warning everyone to vacate the beach. I recall that the acridity in the air effected breathing. I hope that Tenerife is not sleepwalking to similar problems.

  7. Yesterday when I was on the highway north joining the highway south I again saw an extended wiite spot (such as milk) just below the shoreline. I’m sure these were not algae. I do not have pictures because you can not stop there.
    The algae are abused and getting way too much attention to hide the real problem, discharges of sewage. Now we all know, time to inform people about how they are going to resolve this envirnmental scandal.

  8. I am confused as what are the beaches that are affected. I am currently in candelaria. I have seen these big brown patches floating very near the shores.

  9. Ask the divers off the coast at Los Gigantes whether the “blooms” are natural or man-made! The treatment of waste from this area is a scandal and has been for years. The problem is that those in charge appear to be in permanent denial.

  10. A little confused on this as I am now reading (social media) that it is not algae but a broken sewage outlet! I have seen this on the surface of the water here in Playa Paraiso and really would like to know the truth as I have been put off swimming in the sea.

    1. Author

      There are several issues, Keith. One is E.Coli on the coast between Candelaria and El Médano – the incidents are being investigated but all beaches are currently clear. Another is the algae, which was a temporary “blooming” due to the heatwave and it is now dissipating in any case – and was only an issue if a major outbreak moved into the coast. This was a matter with potential effects in the whole of Tenerife.

      Yet another issue is the all-too-frequent breakages on pipes/sewage outlets. These are by their nature temporary and unforeseeable and (hopefully) are dealt with quickly as and when they occur. I know of no specific current warning concerning any beaches in Adeje municipality.

      Generally the best advice is to take confirmed information from official sources or trusted media outlets.

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