Lake Stymphalus and its monstrous birds

Lake Stymphalus he was at the foot of the mountain Cylene In the lower part of the valley, there two rivers drained through catavotras (channels), after a 35 km underground channel they reappear outside in Argos.
Birds were monstrous creatures from Greek mythology that had the beak, the legs and the wings of bronze. Another of its characteristics was the toxicity of its excrement that destroyed all crops and were carnivorous.
No one could kill them because they defended themselves by dropping their metallic feathers on their attackers and then devouring their bodies if the person was not armed, but if they carried weapons they fled. They destroyed all the crops in the surroundings, they devoured the cattle and the people who passed by the place.
The waters of the lake did not receive sunlight or reflect the stars because it was completely covered by birds.
Euristeo entrusted to Heracles (identified as Hercules By the Romans) 12 jobs and one of them the fifth was finish with the birds of Lake Stymphalus.

Heracles did not know how to carry out this task since there were many birds for his arrows and his forces were not so many as to kill them all. But as always the gods were close by and the goddess Athena who liked to help the great Greek men helped him by giving him a bronze bell whose property was to scare away birds and multiply arrows.
He had to climb the mountain and sound the bell, so they were scared and in their flight Heracles shot them down with his arrow. In this way the lake was freed from monstrous birds.
Today that place is called the Zaraka Valley.