The Wrong One!

Standing at the edge of the lake, a man saw a woman  flailing about in the deep water. Unable to swim, the man  screamed for help. A trout fisherman ran up. The man said, 
"My wife is drowning and I can't swim. Please save her.  I'll give you a hundred dollars." 
 
The fisherman dove into the water. In ten powerful strokes,  he reached the woman, put his arm around her, and swam  back to shore. Depositing her at the feet of the man, the  fisherman said,
"Okay, where's my hundred?" 
 
The man said, "Look, when I saw her going down for the  third time, I thought it was my wife.
But this is my  mother-in-law." 
 
The fisherman reached into his pocket and said,  "Just my luck. How much do I owe you?"