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University of Washington Botanic Gardens


Washington Park Arboretum
Center for Urban Horticulture

Washington Park Arboretum Shoreline

Foster and Marsh Island Notes

Arboretum wetlands photo by E. Welty

photo by Ethan Welty

The Arboretum's Waterfront Trail leads you to Marsh and Foster Islands. Pick up a trail guide, keyed to numbered posts along the trail, at the Graham Visitors Center. If you visit in the spring, look for the blue, scented flowers of China’s empress tree (Paulownia tomentosa). In summer, a breeze may cause "snow" to fall from the cottonwoods (Populus). In the fall, look for golden-hued needles of the larch (Larix).

Many kinds of trees mingle here: willows (Salix species) on the water's edge, an alder grove (Alnus species), the sleek madrona (Arbutus menziesii), pines (Pinus), Douglas-firs (Pseudotsuga menziesii), maples (Acer) and oaks (Quercus). Smaller woody plants such as salal (Gaultheris shallon) and serviceberry (Amelanchier) grow in the understory.

As you wind past Duck Bay to reach Foster Island, watch for American coots, pied-bill grebes, bitterns, blue herons and Canada geese on the water or at its edge. Comorants perch on driftwood washed to the shoreline, while cutthroat trout and sock-eye salmon swim beneath the surface. Goldfinches, bush-tits and song sparrows dart about in the trees. Large marshes, teeming with many forms of life from tiny insects to stately herons, surround Foster and Marsh Islands.

From the northern tip of Foster Island, you can look across Union Bay to the University of Washington campus and Lake Washington. On clear days, you'll catch views of the Cascades and Olympics. From Foster Island, a boardwalk leads westward over the water to Marsh Island. Along the boardwalk, you’ll find native marsh plants, such as cattails (Typha latifolia) and waterlillies (Nymphaea species). Unfortunately, you will also see purple loosestrife (Lythrum virgatum) and yellow flag iris (Iris pseudacorus), both of which are pretty, but aggressive, non-native plants.

Washington Park Arboretum Shoreline Restoration Completed

The Shoreline Trail restoration project is now complete, and the area has once again been opened to the public. Anchor Environmental, L.L.C. was commissioned by the Seattle Department Parks and Recreation as the prime consultant for this waterfront park and habitat restoration project. Designed by the Olmsted Brothers Landscape Architects, the Washington Park Arboretum is one of the largest, and most loved, historic park holdings within the Seattle Parks system.

The park’s shoreline is located on Lake Washington’s Union Bay and contains one of the largest and most significant wetlands on the lake. The area is critical habitat for federally listed species such as Chinook salmon and nesting bald eagles. This wetland is also part of a very popular canoe route, and has a heavily used pathway system along the 1,700 linear feet of shoreline. The general intent of the project was to restore the eroded shoreline as fish and wildlife habitat, while providing access and views for recreation. Access for the disabled was also an important aspect of the trail improvements, which include relocating and rebuilding pathways, and replacing a major pedestrian bridge to Foster Island. As a result, carefully located viewpoints and water access points are designed to focus human use in appropriate locations. Note: canoe landing is permitted at the newly-installed landing areas, but no boat launching of any kind is permitted at the Washington Park Arboretum.

The habitat improvement component of the project is located on a former landfill and marsh. As a result, the design included structural elements and earthwork features that required geotechnical engineering analysis of a bridge as well as shoreline and pedestrian trail regrading. Anchor conducted a program of drilled borings and limited exploratory excavations to establish underlying soil types and their engineering characteristics relative to the planned construction. Anchor then determined appropriate pile types and embedment depths for bridge support, and evaluated the potential for re-use of excavated soils in construction of the re-graded paths. KPFF provided the civil/structural design for the project, including the new bridge.

This project is an element of the Washington Park Arboretum’s Master Plan, developed with public input by Seattle Parks and Recreation, the University of Washington, and the Arboretum Foundation, and approved by the Seattle City Council in 2001.


Last modified:
Thursday, 29-Jan-2015 16:16:59 PST