Are the season transitions a matter of some debate? Here, I think open water swim season is mid/late May to early/mid September. But a friend swam in April and as recently as last week. I'm not convinced she isn't going to get a December swim in as a matter of principle. Eventually ice will force her out of the water. If I had to define seasons: 1. Empty pools, running that has a lot of laundry, indoor cycling, fun hiking. 2. Busier pools, great running, cycling on dirty roads, goopy hiking. 3. Busy pools but open water swimming too, running that makes me question if something is wrong with me, great cycling, hot busy hiking. 4. Quiet pools and great wetsuit swimming, great running, good cycling with layers, great hiking. I might have just realized fall is my favorite season.