There are 2 parts to the trip to the springs. You can fly / boat / kayak to the head of the lake. If water isn't too rough, you should be able to paddle board there, if you know what you are doing.
Then there's the trip from the head of the lake up the Pitt River to the springs. I think you will find that the river runs faster than you can paddle. People do take jet boats all the way up to the spring, but most people cycle the 25 km or so along the logging road.