might have some information for you about the size or the city of Tacoma website or maybe it is Tacoma Power website (I think one of them run the lake).
Sorry Sarah..but I beg to differ about Lk. Sammamish. It is only a step better than Lk. Washington, which is known has a mini ocean.
I won't board Sammamish or Washington if I don't have to and I live (and have a dock) on the Lk. Washington. Within one to two hours of Seattle are several great hidden lakes where I see only one or two boats (plus a couple of lil fishing boats) all day.
If you want to know about a great hidden lake that is butter most of the day with camping available e-mail me and I will give out some secret lake info. Don't want to release them live on the site, don't want to fill them up, then they won't be secret anymore and might get busy. email@example.com