Hardest Swimming Events

Hardest Swimming Event? 50, 100, 200, 500, 1000, 1650, 5k, 10k?
The items in this list have been selected by the author of the list for you to vote and comment on.
The Top Ten
1 50 Freestyle

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2 100 Freestyle
3 200 Freestyle
4 500 Freestyle
5 1000 Freestyle
6 1650 Freestyle
7 5k
8 200 Fly

Hardest By FAR

9 10k
10 100 Fly