Yep, it's most likely the annual mayfly hatch (about 3 weeks early this year) and whitefish feeding.
It's one of the highlights of the year for me on my lake in QC.
Pretty much the only time of year when you can catch whitefish on dry flies.
Years ago when I first attempted to catch them I missed half a dozen wicked hits. Big splashy boils where my fly dissapeared. I'd set the hook and...nothing.
It took a while to figure out, but the whitfish were either slapping at my fly with their tails or pushing it with their snout to submerge the fly.
Once the fly was submerged they'd suck it in with their underslung mouth.
So after missing the first 6 and clueing in I began to catch them.
You'd have to force yourself to wait 3-4 seconds after the initial rise (not easy to do) then gently lift up on the rod.
Caught a bunch that way.
On my lake the mayfly hatch usually occurs last week of June/first week of July but apparantly it's starting right now as well.