At the start of an open water event, watch out for hot dogs coming up behind you.
The start of an open water swim is always tricky: scores of swimmers are diving in together and heading for the same distant buoy. There's a lot of bumping, accidental kicking, and thrashing.
To avoid the mayhem, line up on the far outside of the starting pack and angle toward the turn buoy. After 100 yards or so, the group will have separated and you can find all the open space that you need.