What does Meryl Streep say in the water at end of mama mia?

Meryl Streep, as Donna Sheridan, does not say anything in the water at the end of "Mamma Mia!". The scene you're likely referring to is the final one where Donna is on the beach watching her daughter Sophie marry Sky. Donna is smiling and happy, but she doesn't speak.

This scene, while not containing any dialogue from Donna, is incredibly powerful and symbolic. It signifies the passing of the torch from Donna to Sophie. Donna has found love and acceptance of her past, and she is now ready to let Sophie go and start her own life.