He feuded with his brother, Baal, god of fertility. Yam-Nahar was the god of the sea and rivers, and Baal disliked Yam-Nahar because he believed that El favored him.
This creature was said to be a sea dragon with seven heads. Yam-Nahar did not live very long, as Baal killed him when he was still young. 
It is said that, while this creature was a sea serpent, it also boasted seven heads.
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