Sullie,
I think if you are in Snohomish and head out Machias road and then take a right on either 3 lakes road or the next main road up Machias, you'll find signs to Flowing Lk. There is also a golf course there, so there should be signs to that as well.

I have never been to the launch, so I can't get you much closer than that.

If you are coming from I-5/HWY 2, that's the way I'd go. You can get off hwy 2 @ New Bunk Foss RD. just after the Bickford exit. Head N or Hwy 9 to Bunk foss rd. and turn right.

That road winds you down to Machias road, where you turn R to get to 3 lakes Rd.

I'm sure someone else can get you closer than I can, but thought I'd at least get the conversation started.

Jeff