Funny Blonde Joke

"Out in the sea a ship sank. The only survivors were a brunette, a red head and a blonde. The only choice they had was to swim 100 metres back to shore. The brunette left first and swam 70 metres but she drowned. The red head left second and swam 80 metres but she drowned. The blonde was last and she swam 50 metres but she got tired and swam back."