Near the island of Zakinthos , a group of swimmers came across what appeared to be a submerged lost city in 2014. There were paved floors and columns. However, apart from these architectural remains, there was no sign of human presence in the city, such as coins, vessels and the like.
A special section of the Greek Ministry of Culture and Sports, specialized in underwater archeology, after analyzing the supposed lost city has discovered that it is a city, nor is it lost. In reality we are dealing with buildings produced by bacteria and a natural geological process .

This is what has revealed an analysis by microscopy, X-ray and analysis of isotopes that has been published in the journal Marine and Petroleum Geology . According to Julian Andrews , first study author and researcher at the University of East Anglia, UK:
We investigated the area, which is two or five meters deep, and discovered that it is actually a geological formation. The disk and donut shapes that were found, and that were confused with the column bases, are the typical product of a hydrocarbon mineralization phenomenon, which appears on both modern and ancient sea beds. The strange formations are the result of a fault (hence the more or less straight distribution) that did not completely break the seabed. That fault released gases, especially methane, from the depths. Microbes in sediment use carbon from methane as fuel (food source). They oxidize the methane and cause changes in chemistry that create cement-like sediments, which geologists call "concretions."
Via | ABC