The fishing season runs November to April — this is the primary travel season for Junín. November and December are excellent months: the rivers are full from snowmelt, the fish are active, the araucaria and lenga beech forests are green, and the days are long. March and April are autumn and bring spectacular colour to the forests, with the lenga beech turning gold and the piñon harvest underway.
Summer (January–February) is warm and busy — school holidays bring Argentine families to the lakes and mountains. The fishing is good but the rivers can be lower and warmer by late February.
The park is open year-round but winter (May–October) is cold and many services in the town reduce hours. The ski resort at Chapelco (near San Martín) attracts some winter visitors, but Junín itself is quiet. The Lanín volcano summit is climbed mainly in January–March.