ויאמר ה’ אל משה אמור אל אהרן קח מטה ונטה ידך על מימי מצרים (וארא ז:יט)

Rashi says that since the river protected Moshe when he was placed in its waters as a baby, Aharon was assigned the task of hitting the water with a staff to bring upon the ‘Makos’ – plagues,  since Moshe felt that hitting the water would show a lack of appreciation.

We learn from here the Middah of “Hakaras Hatov” – acknowledging someone who did good to you.