In case you're visiting London and need a place to swim...

I think one lane swims clockwise, the adjacent lane swims counterclockwise. Minimizes the chance of collisions, since the swimmer just on the other side of the lane line from you is going in the same direction as you.

I think one lane swims clockwise, the adjacent lane swims counterclockwise. Minimizes the chance of collisions, since the swimmer just on the other side of the lane line from you is going in the same direction as you.