Dan,
I think the area you are referring to is the Mottman holding ponds. It
is an area that is designed primarily for storm runoff, but it's a great place
to check for birds.
To get there from Seattle, take I-5 South and transition to Hwy101 North.
(It's the only way you can go on 101 at this point). Take the second exit,
Black Lake Blvd. Get in the left lane on the offramp and turn left on Black
Lake, go under the freeway and continue for about 1/2 mile. Turn left just past
the BP gas station onto Mottman Road. The ponds will be to your right. You
will find the best place to park if you continue another few hundred yards
around the curve and park just on the other side of the railroad tracks.
Good birding!

Jeff Zuckerman
Olympia, WA
360-754-4083