I've been looking online for info about LK WA and Sammamish. I can't seem to find anything actually related to  lake Sammamish except for the surrounding land. I've found some good stuff on landslides at WA though, a while back, that has been helpful. I've found out all kinds of stuff from reading about WA but can't get anything on Sammamish. Can anyone help me out? I really wanna know how the underwater forest got there, and find some other anomolies etc. 

Yeah I found that part after sifting thru many pages of crap related to real estate, and historical sites in the surrounding area. I've been able to find a few good articles but you have to go thru a ton of non related ones to find a good one. So as an answer to your question, An Earthquake happened about 1000 years ago that caused a few major landslides. The trees, some remaining upright, slid down and ended up in the lake, the same way they did on the south end. Also there have been two other major quakes each seemingly 300 years apart, that may have caused the other trees to slide down the hill into the lake. The water actually preserves the trees quite well, thats why you can see them on the surface; because the part that sticks out is exposed to the elements and rots away.

It's amazing what you can find online when you're stuck inside on a snow day!   

By the way its been about 300 years since the last landslide, I think we're overdue for another.