Yes, as far as I know it is part of Deception Pass State Park, so a discover pass is required beyond the WDFW parking pass. It's very confusing, and not very clear, but Pass Lake doesn't show up on the WDFW water access site for Skagit county: http://wdfw.wa.gov/lands/water_access/county/Skagit/
I'll back the other posts, gotta have the Discover Pass to park at Pass Lake. The main launch area is on State Parks land, and is not controlled by the WDFW, so it's either a $10 day access or $30 yearly access for the Discover Pass. The WDFW parking pass doesn't cover you at Pass.