River is not deep

A stranger on horse back came to a river with which he was unfamiliar. The traveller asked a youngster if it was deep.

"No", replied the boy, and the rider started to cross, but soon found that he and his horse had to swim for their lives.

When the traveller reached the other side he turned and shouted : " I  thought you said it wasn't deep ? "

It isn't, was the boy's reply : '  it only takes grandfather's ducks up to their middles ! "