There’s a nice article here about summer ales and Maine’s growing homebrewing and microbrewing scenes.
The beauty of summer ales is that they don’t really exist, as a historical style of beer, so they can be whatever the brewer wants them to be.
Petersen, for instance, makes a summertime watermelon lager, with Vienna malt, German lager yeast, Irish moss, and pureed watermelon….
The term "summer ale" is largely a marketing term created by microbreweries a decade or so ago, when they sensed that their customers liked the idea of seasonal ales, that is, a different beer to try every few months.
I really need to homebrew again; this is a good article to get thinking about all the various possibilities you can take advantage of when formulating a beer…