Kinneret Invaded - by Leeches

Leeches have invaded Lake Kinneret's shores - for the second time in seven years.

Standing in the water for as little as two minutes will cause your legs to be covered in hundreds of leeches. These particular types are not blood-suckers, making them relatively easy to remove once one is out of the water.

They are found on the lakebed, at depths of 0.5 to one meter, at two spots over the last few days: near the Sapir visitors center and along the western coastline. They live off snails and other invertebrates.

The leeches first overran the shores of the lake seven years ago.

Four types of leeches are known to live in the Kinneret, but they are usually present only in small numbers. This year, however, huge quantities have been detected.

Dr. Tamar Zohary, director of the Kinneret Limnological Laboratory, said that in 2010-2011, her lab conducted a comprehensive survey of the lake's leech population at 17 different locations along its coast, and found only a handful of leeches.

Why the numbers suddenly exploded in 2005, and again this year, remains a mystery.

However, this appears to be further proof that the Kinneret's ecosystem is less stable that it used to be. Several years ago, when a new species of alga appeared in the lake, Zohary told Haaretz that until the mid-1990s, the alga population had been completely predictable, and the new species' appearance thus signified growing instability.

Another example of this instability was the sudden appearance of Thiara scabra, a species of snail whose native habitat is East Asia.

Thiara scabra quickly came to dominate the lake, and now accounts for 95 percent of the Kinneret's total population of molluscs.

The type of leech now flooding the Kinneret's shores feeds on Thiara scabra.

The main explanation for the lake's state of flux is human activity, including pollution, poisoning and overpumping.

The cumulative effect has been to produce much greater variations in the water level: In the past, the difference between the Kinneret's highest and lowest level was about 1.5 meters, but today it is as high as six meters.

This fluctuation in the water level is one proposed explanation for the surge in the leech population.

By causing a sharp decline in the snail population, which preys on leech eggs, the rapidly changing water level has increased the number of leeches born, according to that theory.