Just south of downtown, Mercer Slough is Lake Washington's largest remaining wetland — 320 acres of marsh, bog, and riparian forest threading through the middle of a dense suburb. The Mercer Slough Trail and boardwalk allow exploration without mud, passing blueberry farms that have operated in the slough since the 1940s, and several viewpoints over the open water where herons, egrets, and the occasional bald eagle fish.
The park is busiest on the Blueberry Farm Trail in August, when u-pick farms open along the slough edges. Outside harvest season it sees far fewer visitors despite being one of the best urban wetland walks in the greater Seattle area. Canoe and kayak rentals are available from a small outfitter at the park trailhead.