Summer (June through September) is the main season for fishing, hiking, and exploring the backcountry. The weather is reliably warm, Borestone Mountain is accessible, and the rivers are at good levels for paddling and fishing. Fall foliage in late September and October is spectacular in this corner of Maine — the mix of hardwoods and lakes makes the colour particularly vivid, and the crowds are a fraction of what you find further south.
Winter brings serious cold and deep snow, but also a thriving snowmobile culture; the trails in Piscataquis County are among the best in New England. Spring is the problem season: mud (April in particular) can make dirt roads impassable, and some trails to trailheads are not accessible until late May. If you are planning a spring trip, check road conditions carefully before heading out.