The good news is that the brook trout were feeding. Hatching insects thickened the air above the water. Rising fish hammered aquatic insects as they emerged from the bottom of the stream, or later as they hovered low over the water, or later still as they fell back down on the surface to lay their eggs.
The bad news is that most of the insects were mosquitos, and some were black flies. 
That’s life chasing brook trout in New England in late May and early June.
It began with two afternoons at one of my favorite mountain lakes in Addison County. On the first afternoon, I was with a friend, and because of his schedule we had only a couple free hours for the entire excursion. By the time we bumped and skidded several miles down the dusty gravel forest road, and then hiked nearly a mile through the woods, most of those two hours were gone; I had only 30 minutes left to actually cast before we would have to turn around and head back out.
The alpine water I was fishing has only a narrow window every year when I can catch trout by fly-fishing from the shore — when the water temperature is warm enough to induce a heavy hatch of insects, but still cool enough for trout to be near the surface, and when the stream flowing into the lake still has enough water to attract fish out of the deeper lake and into the flowing inlet or at least close enough into the shallow water to reach them from the shore.
It turned out I had hit that narrow window perfectly, and those 30 minutes proved enough time to land six brook trout. We arrived at the water to find clouds of insects hovering over the surface of the water and swarming the woods along the shoreline. They were mostly mosquitos, but a few mayflies and caddisflies were mixed in, and I even saw one small golden stonefly commonly called a yellow sally flutter past me.
Of course the moment we stopped hiking and stood still on the shoreline, the swarm discovered my exposed flesh and I had to start swatting. I hoped the trout were as impressed with the swarm as I was. I saw no feeding activity on the surface, so I tied only a small nymph and began to fish below the surface. On my second cast, as I drifted my nymph through a likely area, I landed a fat brook trout. Three or four casts later I landed a second.
Then I noticed fish beginning to rise. I clipped off my nymph and tied on a dry fly — a little generic pattern that can be used to imitate a variety of small insects. In the next 20 minutes I landed four more and lost one or two others. My friend, who doesn’t fish, watched in amazement. It was the sort of near-constant fishing action, with trout taking flies right off the surface, that turns non-anglers into anglers. It was also the sort of non-stop mosquito-swatting that turns anglers into non-anglers.
Still it was our time constraints more than the biting insects that drove me away from the water. And my expedition had gathered the intel I wanted. I determined to return the next day.
When I came back the following afternoon I had both more time and also more insect-repelling clothing covering my body. Nonetheless, between the time I arrived from my hike and the time I was able to dig that extra clothing out of my little backpack, I probably killed a dozen mosquitos. I killed another dozen or so while I tied on a fly.
Then it was all fishing. I landed a couple fish where the small tributary stream flows out into the lake. When I noticed little dimples begin to dot the whole surface of the pond, I left the stream and waded out knee-deep into the lake. From just a few yards away from the shore, I was able to reach the rising fish with my casts. For the next hour I was laying dry flies on the flat surface of the pond every place I saw a rising fish. One out of five casts produced a fish. An occasional breeze coming across the water even drove the mosquitos off me for several minutes at a time.
Only a weekend later I was out of Vermont and visiting my brother in Maine. We had a couple days together at the end of the long holiday weekend to tromp around the vast territory around the famous wild brook trout waters of western Maine that we have been fishing together for decades. We decided to spend one day exploring two less-famous rivers we have driven past scores of times and wanted to fish, but never actually got out on, and another day dealing with crowds on a more famous trophy wild trout water.
When we pulled the car off the road on that first afternoon, and before we could even get into our waders, we had so many mosquitos humming around the back of our Subaru, I knew we were in for some archetypal late May New England brook trout fishing. I was not wrong.