Trout
Flyfishermen are fond of reading calendars and published hatch charts. Bugs and trout, however, are not just illiterate but inconsiderate, too. Things don't always happen when they're supposed to, the best-laid vacation plans notwithstanding.

Nationwide, trout fishing patterns vary enormously by region in early summer. Major rivers in the East and Upper Midwest usually have settled flows and major evening fly hatches by mid-June, while many Rocky Mountain rivers are sometimes high and flush with snowmelt until late in the month. By mid-August, though, regional fishing conditions have caught up with themselves. In late summer, you'll be catching Wyoming trout with the same techniques that anglers are using in upstate New York. But there is good fishing to be had almost anytime. You just need to pick the right spots and tactics.