A significant brown discolouration in the ocean triggered alarms on Friday in the southern region of Tenerife. Felipe Ravina, a graduate in Marine Sciences, indicated that this was a “mega spill” that affected Troy beach in Adeje and Las Américas beach in the municipality of Arona. The communicator, who has documented the consequences of submarine discharges in the Canary Islands through various audiovisual productions, noted that despite the polluted water and unpleasant odour in the vicinity, no access points were closed.
In the meantime, he reported that hundreds of individuals continued to swim in the water. “Public health is jeopardised, and we cannot overlook the significant harm caused by a spill of this nature to marine ecosystems,” he stressed in a post on his social media channels.
That same afternoon, the Cabildo de Tenerife asserted that the source of the discolouration was related to construction work in Costa Adeje aimed at establishing a seawater collection well, part of the approved actions to secure the water supply in the southern area of the island.
Official statements revealed that, during drilling, technical equipment encountered a seawater table, “which resulted in the temporary release of seawater externally.” “It is exclusively marine water, devoid of any pollutants. It is not a discharge or wastewater leak,” emphasised the island’s governing body.
A broken pipe in the treatment facility
The announcement made no mention of another incident recorded on the same day in the area, which, according to sources from the Cabildo, is unrelated to the pollution detected along the coast. Last Friday, April 25, a pressure loss was also noted in a pipe at the wastewater treatment facility (EDAR) of Adeje-Arona, located four kilometres from the beaches where the stain was observed.
“The emergency protocol was triggered, and water was redirected from another parallel pipe until the issue was rectified,” these sources indicate, adding that the breakage was resolved overnight. However, they refute any claims of a discharge occurring. “The pumping ceased, and the damaged section of pipe was repaired,” they stated.
In this regard, sources reiterate that the water evacuated through the pipe was “pre-treated” and contains no faecal matter or contaminants. In the wastewater treatment process, pretreatment is the initial phase. During this stage, substances that may cause issues in subsequent treatments are removed. It is in the primary treatment that various solids begin to be eliminated, while the secondary phase addresses water pollution, as detailed on the official website of the Ministry of Ecological Transition.
Julio Muñiz Padilla, a Chemist, Physical Scientist, and Specialist in Curs and Environmental Emissions, explains that the pre-treated water “has merely had the larger objects removed.” “Perhaps it underwent a minor settling process, but that water has dissolved all organic matter and bacteria. If the saline concentration is low, the entire beach remains contaminated,” he clarified in remarks to this publication.
This publication has inquired with the City Council of Adeje regarding whether a water analysis of Troy beach was requested last Friday. The corporation responded that the Insular Water Council “provided a 100% guarantee that it was treated clean water,” hence “it was deemed unnecessary to conduct any type of analysis.” Additionally, these sources indicate that “the spill” had a greater impact on the municipality of Arona. The City of Arona has merely remarked that “the action falls under the jurisdiction of the Insular Water Council.”
The spill in Tenerife
Expert Julio Muñiz clarifies that, aside from the runoff, discharges into the sea can be categorised into three types: sewage, treated waters, and the rejected waters from the regeneration process. “Fecal waters are highly polluting and illegal in nearly all discharges unless they occur at a distance exceeding 500 metres. The law still permits the disposal of these contaminated waters to take place through diffusion in the sea, which is a significant issue in the Canary Islands,” he explains.
In the case of Lanzarote and Fuerteventura, as they are islands with a “quite large” shelf, submarine outfalls should be considerably larger. “This does not occur, or if they exist, they are often damaged,” he elaborates.
Directly at the location where the spill was reported, the Adeje-Arona submarine outfall is found. The Insular Water Council invested over four million euros in April 2024 to extend it by 200 metres, positioning it 1,100 metres from the coast and at a depth of 40 metres. This pipeline channels wastewater through the Trojan ravine.
The physicist indicates that the most common discharge is that of treated waters, which are subsequently diverted to the sea. “The law mandates that these waters must be free from bacteria, yet the treatment process itself does not entirely eliminate them,” he highlights. “In most treatment plants where water is not reused, the hydrological plans being developed across the different islands aim towards the reuse of already treated wastewater for agricultural purposes, which is a misnomer they prefer to call a circular economy,” he critiques.
“When they state that this new system will not discharge water into the sea, it is misleading. Even if water is utilised for agriculture, a portion of that water, along with all the problematic nutrients it contains, will reach the sea,” he summarises. Of the 100 litres of water entering the treatment facility, the chemist explains that approximately 60 will be used for agriculture. The remainder will flow into the ocean.
Furthermore, when the water released into the sea originates from desalination plants, it contains “double salt.” “To obtain one cubic metre of potable supply water, two cubic metres of seawater are required. The remaining cubic metre has twice the salt concentration and, during the process, sulfuric acid is added,” states the chemist.
This excess is denser than seawater, and due to the presence of highly aggressive chemicals, it does not float but instead sinks to the seabed, thereby destroying seagrass meadows. The Canary Islands have already lost half of these habitats, with nearly two kilometres of these marine environments vanishing each year, according to a study by the University of Las Palmas de Gran Canaria.
Such discharges “are immensely destructive, yet they remain invisible.” “They leave no discernible trace,” Muñiz points out. Regarding the situation in Adeje and Arona, the expert suggests, “It is highly probable that it involves water with a significant amount of sewage, and that through some process, the runoff or sewage waters have inadvertently mixed,” he states.
