Why you should avoid swimming in bright green water (even if it's Insta-worthy)

Swimming in the sea is said to be very good for us but that doesn't mean it comes without any risks.

As long as you avoid shark-infested waters or any of the other terrifying animals you can find in the ocean or on the beach, your life is unlikely to be at risk if you're a strong swimmer or someone who sticks close to the shore.

However, much like avoiding the yellow snow, scientists have issued a warning about the green waters which appear annually at a popular tourist hotspot in the Philippines.

Although the Philippines is regarded by many as one of the nicest places on Earth to visit, and that comes from people who have visited every country in the world, it seems as if you might want to play it on the safe side when it comes to Boracay.

The world-renowned island in the Philippines is famed for its white beaches and crystal clear waters yet often between February and May, the waters are more green than turquoise because of the algae that appears.

Now, it's nowhere near as bad as swimming in the Thames might be but the claims that it's perfectly safe might be a little off the mark, if the opinions of some scientists are to be believed.

"A number of macroalgal species, including green macroalgae (or seaweeds), can be seasonal. Their seasonal occurrences are related to certain environmental factors (both natural and anthropogenic), e.g., water temperature and availability of inorganic nutrients. The seasonal occurrence of certain macroalgal species is more prominent in cold-temperate and polar regions (where there are four distinct seasons).

"However, this can also be observed in tropical countries like the Philippines during different monsoon seasons and/or dry/wet seasons where a few degree increase in temperature can trigger the reproduction of certain macroalgal species, and the inflow of terrestrial-derived nutrients from rainfall can fertilise the coastal waters with the required inorganic nutrients (nitrogen and phosphorus) to trigger green algal blooms, among others," Dr. Michael Roleda, a professor at the University of the Philippines told Esquire Philippines.

When the algae appeared back in 2015, scientists suggested to indy100 that it could well be caused by pollution.

The resort was closed for six months back in 2018 (NOEL CELIS/AFP via Getty Images)

Videos and reels have emphasised that the algae has returned again in 2026, and Dr Roleda noted that the algae has more recently been attached to rocks, something which he believes means that it is thriving in an ideal environment.

Roleda added: "Macroalgae propagules (microscopic spores and gametes) are floating suspended in the water (just like seeds and pollens flying on air), and when they touch down on the hard substrate, they attach, germinate, and grow, and bloom depending on the available resources (nutrients, temperature, light). The question is, is the source of nutrients natural or anthropogenic? If anthropogenic, then we have environmental issues."

Anthropogenic essentially means that their formation and later reproduction is caused by human intervention, which would likely point towards excess waste in the water.

The doctor concluded: "The presence of algae on hard substrates is natural. Their huge standing stock/biomass or their intensity of blooming can indicate either natural and/or anthropogenic sources of nutrients during months when algal propagules are readily available for recruitment/establishment under suitable temperature and light regimes."

So to put it in terms that we're all more likely to understand, if the algae in the sea there is in indeed anthropogenic, then it's probably not the best time to go for a dip.