Coming from either Cairns or Atherton, Lake Barrine is very easy to find.
From the Gillies Highway, the Lake is less than a minute from the highway, marked clearly in both directions.

Getting There From Cairns

Approximately 5 minutes after reaching the top of the Gillies Highway, turn left at the “Lake Barrine National Park” sign

Getting There From Atherton

Follow the Gordonvale Atherton Road. Approximately 8km past Yungaburra, the turnoff to Lake Barrine National Park should be clearly signed on your right.