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Summer may officially be winding down, but in Cyprus, September and October can be some of the best months to head to the beach. The crowds begin to thin, the sea remains warm, and the intense heat becomes a little easier to handle.
But before diving in, many swimmers find themselves asking the same question: Can you tell simply by looking whether the sea is clean and safe?
Cloudy water, foam, bubbles, or a rainbow-colored sheen on the surface can all make us hesitate. At the same time, sea urchins are often seen as proof that the water is clean.
So, what do these signs really mean?
According to an article published by OW.gr, environmental scientists and oceanographers, including Maria Eleftheriadou, an associate at the University of the Aegean’s Department of Oceanography and Marine Biosciences, explain which signs may offer useful clues and which can be misleading.
Sea urchins: Usually a good sign, but not a guarantee
Sea urchins are often associated with clean water, and there is some truth to that. They are relatively sensitive to pollutants and play an important role in maintaining the natural balance of the marine ecosystem.
Their presence, however, does not automatically mean the water is pollution-free. Likewise, their absence does not necessarily mean the sea is dirty.
Sea urchins may be missing from perfectly clean waters because of overfishing or other environmental factors that have affected their population.
Jellyfish: Not proof of either clean or dirty water
The presence of jellyfish cannot, on its own, tell you whether the sea is clean or polluted.
Jellyfish can appear in healthy marine ecosystems. However, they also thrive in warmer waters, which in some cases may be linked to wider environmental changes.
In short, spotting a jellyfish may be unpleasant, but it is not necessarily a sign that the water is unsafe.
Moon jellyfish: A possible warning sign
Transparent jellyfish from the 'Aurelia' family, commonly known as moon jellyfish, may sometimes be associated with warmer waters, higher levels of zooplankton, and conditions that could be linked to pollution.
Still, identifying jellyfish species is not always easy for the average beachgoer, making it risky to judge water quality on this sign alone.
Algae and seagrass: The type matters
Not all green growth in the sea means the same thing.
Certain algae, such as *Ulva*, also known as sea lettuce, can be linked to high levels of nutrients in the water and possible pollution.
Posidonia oceanica, on the other hand, is a marine plant with long, ribbon-like leaves. Its presence is considered a strong sign of a clean and healthy marine environment.
Those brown leaves that wash up on Cyprus beaches may not look particularly inviting, but they are often part of a healthy and important underwater ecosystem.
Bubbles and foam: Not always a reason to worry
Foam on the surface of the sea can have several causes.
It may come from detergents or sewage, which would be a warning sign. But it can also be caused by a natural increase in phytoplankton or simply by waves stirring up shallow water.
If the water remains clear and the seabed is visible, there is usually no immediate reason for concern.
Rainbow-colored patches: Take them seriously
A rainbow-like or oily sheen on the water’s surface can indicate the presence of fuel, hydrocarbons, or other industrial pollutants.
This is considered one of the more reliable visual warning signs of possible pollution. If the water looks oily or smells of fuel, it is best to stay out and report it to the relevant authorities.
Currents and cooler water: Generally positive signs
A sudden patch of cooler water can actually be reassuring.
It often points to good water circulation and the regular renewal of water in the area, which can help prevent pollutants from becoming concentrated.
Areas with natural currents generally flush themselves more effectively—but swimmers should, of course, remain cautious if those currents are strong.
Smell: One of the clearest clues
Your nose can sometimes tell you more than your eyes.
A smell of sewage, chemicals, or fuel is a strong warning sign that something may be wrong. A neutral or naturally salty sea smell, meanwhile, is generally reassuring.
If the water smells suspicious, do not swim in it simply because it looks clear.
Cloudy water: It depends on the conditions
Cloudy water does not always mean pollution.
In shallow areas, waves and swimmers can stir up sand and make the water temporarily murky. Natural particles suspended in the sea can have the same effect.
In other cases, however, cloudiness may be caused by increased organic matter from nearby discharges. It should therefore be considered alongside other signs, including smell, foam, and anything unusual on the surface.
Official testing remains the safest guide
Nature can offer clues, but appearances alone cannot confirm whether seawater is safe.
The most reliable information comes from official bathing-water tests and monitoring programs. Beach signs, sampling information, and public water-quality results provide a far more accurate picture than sea urchins, foam, or water color alone.
The sea may look crystal clear and still contain substances or bacteria that cannot be seen. Equally, water that appears cloudy after a windy day may be perfectly safe.
So, enjoy Cyprus’ quieter autumn beaches, but when something looks or smells wrong, trust your instincts, stay out of the water, and check the official information.
