What has rivers but no water, ...

A city slicker was driving through the country when he spotted a horse standing in a field. He was quite taken with the animal and so pulled over to ask the farmer if it was for sale.
"Afraid not," said the farmer.
"I'll give you a thousand pounds!" said the city fella.
"I can't sell you that horse. He don't look too good," replied the farmer.
"I know horses, and he looks fine. I'll give you two thousand!"
"Well, all right, if you want him so bad."
The next day, the man returned the horse, screaming that he had been conned. "You sold me a blind horse!"
"Well," said the farmer, "I told you he didn't look too good."