The 'LSE-101' Curriculum:
Pool Etiquette Overview
General Awareness
Entering the Pool
Passing & Being Passed
Common Sense

Comments welcome!
art[at]cartegic[dot]com

My other projects: 
Financing the swim habit
Endurance fun on land

Other Resources:
Bill Haverland's incredible Swimmers Guide Online - the most comprehensive listing of lap-friendly swimming pools all over the world.

Swimmers arriving at a pool should do three things before getting in the water:

1) Make note of “Fast, Medium, and Slow” lane designations.  If such signs aren't obvious at your pool, ask a lifeguard.

2) Spend a few minutes observing and roughly timing the per-lap pace of swimmers already in the pool.

3) Select a lane containing swimmers moving as closely as possible to the pace that one realistically expects to swim throughout his or her entire workout.

It is the responsibility of the swimmer entering a lane to inform all incumbent swimmers in that lane of their desire to change format (i.e. from ‘split’ to ‘circle’ swimming or vice versa).   Be patient, as this may take a few minutes.  

A swimmer entering a lane being ‘split’ by two people (each swimming up/back on their own side) should be sure before s/he begins to swim that s/he alerts both individuals to the need to change to a ‘circle’ format (everyone swimming counterclockwise* on the right side of the lane).  This is most commonly done by sitting at/on the edge of the pool, waving a kickboard under water, or standing in the water in the corner of the lane. 

When entering a lane with only one swimmer, the arriving swimmer should still notify that swimmer of his/her presence before starting to swim, and explicitly agree with him/her on which format to use (circle or split).

Entering swimmers should allow incumbents a few laps before expecting them to stop.  Incumbent swimmers have an initial right-of-way, but not a right to ‘own’ the lane indefinitely or to insist on their own idiosyncratic rules.

*Note: in Commonwealth countries such the UK, Australia, New Zealand, South Africa, etc., the 'circle' convention is often (but not always) reversed, i.e. swimmers stay to the left of the lane and swim clockwise, or 'anticlockwise' - as is true of automobile traffic and rotaries/roundabouts in those nations.  For foreign drivers and swimmers, this can take some getting used-to!  Adding to the variety (and making it all that more important to observe before starting to swim), many pools in the UK, alternate clockwise and 'anticlockwise' lanes, so that swimmers in adjacent lanes are always swimming parallel to one another rather than in opposite directions.  This has the benefit of reducing the number of smashed hands, punches to the eye, and dislocated shoulders that can occur in collisions between oncoming swimmers whose wrists have the misfortune to lock together at the top of their opposing strokes.