речки

In a sentence

• Дети играли у маленькой речки.

  The children were playing by the little river.

  Here, 'речки' is in the genitive case referring to the possession or location related to 'речка' (small river).

• Жители города заботятся о чистоте речки.

  The residents of the city take care of the cleanliness of the river.

  In this case, 'речки' is in the genitive case, indicating the subject of concern, the river 'речка'.

• Они построили мост через речки.

  They built a bridge across the rivers.

  Here, 'речки' is in the plural nominative case, referring to multiple rivers.