Washington State does have some spatial data for lakes and limited amounts of bathometric data which is really what you are looking for. I downloaded their lake data from the WA DNR site and loaded it into my GIS software. Turns out there are 19 lakes named Long Lake so I would need more data before I could help. You could import a jpg or pdf if you have a scanned copy. I have done it but it sure is time consuming to trace. Most times the create vectors in VCP from a scanned copy is more fixing and time consuming that just heads up tracing. If someone has a digital copy of something that is the way to go.
What I have done in the past is load bathometric data into gis software, select the desired lake with all the bathometric contours and export as a dxf. Load that into VCP and after sizing for the board figure out how deep to make the lake on the board. Say you have 7 contours then to fit on a 4/4 board you could go in 1/8" increments for each pocket. I would start with 0 depth and pocket inside the line to .125. The next contour I would cut a pocket of .125 starting at a depth of .125. Then the next pocket with a depth of .125 starting at a depth of .25, keep repeating until you get to the last contour which represents the bottom.
I would welcome comments or suggestions with VCP ver.9 on how I could make them smooth sides on the lake rather than the steps of each contour. Any thoughts or ideas would be appreciated.