It can be both. Jezero was named Jezero because it's next to the jezero. Edit: Same as e.g. Volgograd (wet town), which is next to the Volga river, named Volga

It can be both. Jezero was named Jezero because it's next to the jezero. Edit: Same as e.g. Volgograd (wet town), which is next to the Volga river, named Volga because it's wet.