Else Beekman
A large brown stain in the sea between the popular tourist areas of Adeje and Arona sparked alarm on Friday, after a marine science graduate denounced what he called a ‘mega discharge’ into the ocean.
Despite complaints of foul smells and murky water near the busy beaches Playa de Troya and Playa de Las Américas, local authorities did not deem water quality testing necessary.
Felipe Ravina, a marine sciences graduate known for documenting the environmental impact of underwater pipelines in the Canary Islands, shared images of the slick on social media. According to newspaper El Diario he criticised the authorities for not closing the beaches. He warned them that ‘public health is at risk’ and that such discharges seriously damage marine ecosystems. Swimmers were still in the water at the time.
Authorities claim it was seawater
The Tenerife Island Council (Cabildo) issued a statement that same day, attributing the slick to drilling works in Costa Adeje linked to the construction of a seawater intake well. Paradoxically, this is part of broader infrastructure efforts to secure the water supply in southern Tenerife.
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According to the Cabildo, the drilling accidentally breached a saltwater aquifer. Consequently, leading to a temporary release of ‘clean marine water’. Officials insisted it was nót wastewater and that there was ‘no contamination involved’.
Concurrent issue at local wastewater plant
However, the same day also saw an incident at the nearby Adeje-Arona Wastewater Treatment Plant (EDAR), located four kilometres from the affected beaches. According to the Cabildo, a drop in pressure was detected in one of the pipelines. An emergency protocol was triggered and the flow was redirected via an alternative pipe. The damaged section was repaired later that evening.
Officials maintained that no spill occurred, stating that the plant’s pumping system was halted and that the water involved was ‘pre-treated’, not raw sewage.
Experts question the safety of ‘pre-treated’ water
Julio Muñiz Padilla, an expert in water treatment and environmental emissions, explained to the press that pre-treatment only removes large debris. “The water still contains dissolved organic matter and bacteria,” he said. “If the salt content is low, those bacteria can survive and contaminate the beach.”
Despite public concern, the Adeje council confirmed it did not request water quality tests, citing assurances from the Island Water Council that the discharge involved only clean water. Arona’s local government redirected inquiries to the same council.
Ongoing wastewater issues in the Canary Islands
Environmental experts have long warned about chronic issues with marine discharges in the Canary Islands. Muñiz explained that, aside from natural runoff, discharges usually consist of untreated sewage, treated wastewater, or brine from desalination plants.
Treated wastewater, while legally discharged, still poses risks. “The law requires that it’s bacteria-free, but the treatment process doesn’t eliminate everything,” he said. Often, water not reused for agriculture ends up in the ocean. Even reused water carries nutrients that can damage marine life when residuals are flushed out.
In the case of desalination, the brine produced contains twice the salt concentration of seawater and often includes added chemicals like sulfuric acid. This denser, chemical-laden water sinks, harming marine seagrass beds—vital habitats already disappearing at nearly two kilometres per year.
Legal limits and outdated infrastructure
Spanish law prohibits direct sewage discharges unless conducted more than 500 metres offshore. However, many existing underwater outfalls are outdated or damaged. The Adeje-Arona outfall, located near the site of Friday’s incident, was extended in April 2024 to a distance of 1,100 metres and a depth of 40 metres, at a cost of over €4 million.
Still, experts warn that even treated water can contribute to long-term ecological degradation. “What they call the circular economy is misleading,” said Muñiz. “Even if you reuse part of the water, a significant portion still ends up in the sea.”
The incident comes during a year already marked by a record number of marine discharge violations in the Canaries.
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