Parts of the northern Adriatic, including Slovenia, have been affected by unsightly marine mucilage, a thick, gelatinous organic matter that has been causing problems to bathers and fishermen.

Although the strong winds mostly blew away the sea snot over the weekend, it has now started to reappear, leaving many a tourist wondering what is going on.

Tinkara Tinta, a researcher at the Marine Biology Station Piran, says this quite rare phenomenon is not directly harmful to people, but can pose a threat to marine life.

Worst mucilage in 20 years

The first records of sea saliva in the northern Adriatic date back to 1729 and the last time it appeared here was in 2018, but this is the first time in about 20 years that it is so widespread.

However, Tinta says that marine mucilage was more frequent in the 1990s.

Sea snot can be a result of a number of factors that researchers are still struggling to comprehend.

The gelatinous organic matter appears when phytoplankton, due to a combination of factors, starts to release large amounts of organic matter or complex sugars into the water.

This dissolved organic matter forms slimy aggregates on the sea surface or in deeper layers of water.

"Along the coast, where the sea is shallow, it can be quickly blown away by a storm, but deeper, it can take a while for it to mix with the water and dissolve, up to one or two months," Tinta says.

"Physically removing the slime from the seabed is almost impossible, but on the water surface people sometimes remove it with nets," she adds.

Bathing not recommended

Although the organic matter does not pose a direct threat to people's health, experts advise bathers to stay away.

The National Biology Institute and the National Institute of Public Health have warned against swimming in the waters affected by sea snot, because pollutants get caught up in the snot.

Rain water and melting snow wash different substances from land to the sea, including microorganisms that can cause disease, and all this gets caught up in the sea snot, they warn.

Sometimes particles such as organisms' skeletons and sediment particles get caught up in the sea snot as well, which can cause skin irritation.

But while this may be unpleasant, sea snot can pose a serious threat to the organisms living on the sea bed and the slow moving animals that are unable to get away from the snot, which can cause them to suffocate.

The snot is also a major problem for fishermen because it gets caught up in fishing nets. Some fishermen do not go fishing at all, while those who do catch almost nothing, fisherman Zlatko Novogradec told the Slovenian Press Agency.

Complex phenomenon

It is assumed that marine mucilage occurs because of nutrients abundance. "This year, heavy rainfall caused rivers to swell and they brought these nutrients to the sea," Tinta says.

Limited activity of bacteria that break down complex sugars and proteins in the sea may also be to blame.

"These bacteria need nutrients such as phosphorus to grow and function, and if there is not enough of these, it is difficult for the bacteria to perform their role as decomposers," she explains.

In summer warmer water rises to the surface and cooler remains down, which prevents the mixing of essential nutrients for these bacteria, the expert says, adding that sea snot occurrence is an extremely complex phenomenon, which will require quite a lot more research work.