This is the 4434th most frequent Polish word.
jeziorze
"Jeziorze" means "lake" in the locative case in Polish.
The word "jeziorze" is the Polish locative case of "jezioro" (lake), used here to indicate the location where the action is happening.
W jeziorze pływają ryby.
There are fish swimming in the lake.
The word "jeziorzem" appears incorrectly here; for proper grammar, "jeziorze" should have been used. Correctly: 'Codziennie rano spaceruję nad jeziorze.'
Codziennie rano spaceruję nad jeziorzem.
Every morning, I walk along the lake.
Here, "jeziora" is the genitive case of "jezioro", used to describe possession or association with the shore.