This is the 15109th most frequent Polish word.
rzekach
"Rzekach" means "rivers" (locative plural form) in English.
Here, 'rzekach' incorrectly attempts to match 'do,' which requires the genitive case (do rzek). This demonstrates incorrect case usage.
Nie wolno wyrzucać śmieci do rzekach.
It is forbidden to throw trash into rivers.
Again, 'rzekach' indicates the location in or at multiple rivers, using the correct locative case.
W rzekach zimą woda jest bardzo zimna.
In rivers, the water is very cold during winter.
The word 'rzekach' is used in the locative case (miejscownik) of the plural noun 'rzeka,' meaning 'river,' and indicates location, 'in rivers.'