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"These kinds of changes in the Kinneret are not an encouraging sign," said a Kinneret expert about an unidentified weed that appeared in the lake. Signs of this worrisome phenomenon appeared about a week ago. It took the form of greenish patches with a foamy train. All those who saw this strange apparition were convinced it was some kind of sewage. What else would one think if one saw a greenish liquid with foam on it? The green patches were sighted on the Kinneret's western shores, from the Tiberias hot springs to the Sapir site.

Researchers at the laboratory which monitors the waters of the Kinneret and inspectors from the lake authority also noticed the phenomenon. After tests were carried out at the Yigal Allon Kinneret Limnological Laboratory headed by Dr. Tamar Zohari, it transpired the foam was coming from new weeds that had taken hold in the water. However, it was the first time the weeds, which created the foam and gave the water an olive green color, had been noticed in the Kinneret and the experts could not identify their exact scientific nature.

The laboratory scientists say foam-shooting weeds have been cited in other parts of the world. "However, we don't know how to define this," Zohari says. She says the reason for the weeds' appearance is not clear. "The conditions were apparently suitable but what exactly these conditions are, we don't yet know because we are not familiar with this species and its biology."

Pinhas Green, head of the Kinneret Authority, says: "In the past two weeks, we've noticed waves of foam and visitors reported this also."

Zohari says that she has seen similar phenomena in the Kinneret before and that this is "yet another example of the fact that the system in the Kinneret is not as stable as it was in the past. Until the middle of the 1990s, it was possible to predict exactly when weeds would appear according to the seasons."

"Since then, we have witnessed phenomena that indicate that this stability has decreased," she says. "For example, the Peridinium weed that used to blossom in the lake every year has since 1996 appeared only now and then, at an inexplicable frequency. At the same time, new kinds of weeds have started appearing. There are also leeches in quantities that we have never before seen."

A growing number of people swimming in the lake have reported leeches attaching themselves to their bodies while they were in the water. The researchers believe the snails that have been badly affected by lower water levels in the Kinneret are responsible for the leeches. The snails have a harder time catching and eating the leeches' eggs, ensuring the latter's survival and population growth.

If in the past, there was a fluctuation of approximately one and a half meters between the upper and the lower levels of the lake every year, now there have been cases where the fluctuation has reached as much as six meters. "This is a significant difference for a system which is used to stable fluctuations," Zohari says.

Green discusses the relationship of decreased water levels and the appearance of the strange weeds: "We have had this kind of decrease in the past and then the weed did not appear. But changes in the Kinneret are not a good thing." Two other man-made factors - illegal fishing and pollution - have also had an effect on the balance in the lake.

But only a few days after they appeared, and even before the researchers had succeeded in classifying them or giving them a scientific name, the strange weeds disappeared from the shores of the lake, leaving behind only the mysterious and worrisome, greenish, foamy patches.