Why use “the” for oceans/seas/rivers etc. but not lakes?

http://english.stackexchange.com/questions/72813/why-use-the-for-oceans-seas-rivers-etc-but-not-lakes

I swam across the Ocmulgee River.
I swam across the Pacific Ocean.
I swam across the Red Sea.
I swam across Lake Winnipeg.

湖名比較特別，不用the. 因為Lake在前，成為一個好像title的字，好像President Obama.