Welts - mixed bag of puddlers. Dog not neccisity, but helps. Can be very crowded on weekends.
Spencer Island - same as above plus its intertidal so the water can get deep quick; watch tides. Small jon boat helps.
Snoqualmie Valley - early is better as 8am rolls around the pheasant hunters start shooting.
Check out the WDFW web site for maps & locales.
Good luck.