How do we know if a sea is clean or polluted?

One of our key questions during the summer, during the holidays, and not only is how we can determine if a sea is suitable for swimming or if it is contaminated. The truth is that it is difficult to see with the naked eye, as it is the germ content that determines whether or not the water is suitable.

Ioannis Chatzianestis, a chemist-oceanographer, director of the Institute of Oceanography, at the Hellenic Center for Marine Research (Hellenic Research Center) analyzes our myths and truths about the purity of the seas.

Does the presence of sea urchins mean that it is clean?

As Mr Hadjianestis explains, there is no absolute correlation as many believe: “First of all, the presence of sea ​​urchins has to do with the habitat of the area, if there are rocks or sand, that is.” The presence of sea urchins does not necessarily mean that a sea is necessarily clear: “There are many factors that can affect the abundance of these species,” he explains.

What about chemical pollution in Greece

“Because we are talking about bathing water the main issue is the microbial load. That is, if there are coliforms and enterococci. This kind of pollution usually has to do with sewage. Chemical pollution that could seriously affect swimmers’ health is a completely different case. In general, in Greece the seas have no chemicals such as heavy metals, hydrocarbons, we do not have a lot of chemical industry, the seas are very clean, ”says the director of the Institute of Oceanography.

Greenhouses and yellows in the water and on the rocks

This is the phenomenon of hypertrophy. Many times we see a “blur” in the water or a greenery on the rocks indicating a high growth of phytoplankton. This means that something in the area is falling, usually fertilizers or pesticides. According to Mr Hadjianesti: “There are many areas that do not have a sewage system so they can sometimes get into the sea sewage.and burden the area. Some substance drops are either organic loads or nutrients from fertilizers that are not necessarily toxic or dangerous. They provide a great deal of food to marine organisms and they are overgrown. It is something that is visible to the eye. And so this phenomenon is created that can be either greenish, yellowish or even red. “

“The danger has to do with what kind of substances have fallen and which ones have already been developed. Often, the subject is aesthetic. Of course, there are also cases where toxic species can develop. Excessive growth may also result in oxygen depletion or hydrogen sulfide odors when these organisms decompose. In Greece it is not that common but there are areas that are happening, such as in Thermaikos for example. It mainly happens in closed seas and has to do with the winds, ”he adds.

Are foam in the sea a worrying sign?

And foaming in the water indicates that we may have an outflow of an organic substance from an adjacent torrent or land. The presence of foams or bubbles, however, is not a safe criterion for rejecting a sea since they may even come from substances of nature.

But even when we talk about pesticides, the risk is low: “To create a problem for people swimming, they have to be in huge quantities,” the director of the Institute of Oceanography explained.

Are seas that have algae clean or not?

Not a few of those who support seaweed are an indicator of purity. On the other hand, some people tend to bathe in seaweed and think they are dirty. What really applies?

” Seaweed is a sign of health” replies Ioannis Hatzianestis. And especially the Posidonians, a classic species in our country, show that the sea is clean. Even the brown ribbons we see in the fall, flooding the beaches and even creating mountains on the coast, are a sign of a healthy ecosystem. Posidonia and algae turn brown when they complete their cycle and are killed. And we shouldn’t collect them at all, it’s good for the region to exist. “

Iridescence on the sea surface

Iridescence may be an indication of the presence of petroleum elements. Oil is visible to the eye even in very small concentrations. The brown color of water, however, can also be the result of excessive development of plankton, as explained above.

As far as the Saronic Gulf is concerned, the Institute of Oceanography which has carried out our studies confirms that since January 2018 there is no evidence of oil contamination of the Holy Zone. Measurements were also made last summer, for precautionary reasons. The general situation in the area is getting better with the clean up of Psyttalia.

Deep-water beaches are preferable to shallows

“In deep waters and in waters where there is heavy traffic if any substance drops, it will dilute very quickly. It is totally different to have a closed and shallow point that has no water circulation and if something falls, there will be a very severe problem. The deeper the waters, the clearer the area will be. Let us also note that the sea has great potential for self-purification, ”stresses Ioannis Hadjianestis.

Avoid places where streams and pipes exist.

The bacteria are found mainly in areas with sewage. The general rule is that we should avoid the places where the pipes are located and the places where the streams are: we should not swim near its mouth.

In addition to the scientists’ advice, it is very useful to keep in mind the research that is published from time to time on the suitability of the coast for swimming. The research of the Hellenic Center for Ecological Research with appropriate and inappropriate beaches in and outside Attica is of great interest.


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