Tacoma, the City of Destiny, was destined to be built on the hills that rise above the western edge of the Puyallup Delta. The Foss probably began as a tidal slough along this edge, fed by the creeks that emerged from the hills to the south and west. In some ways, this is still what it is, albeit straightened, deepened, and devegetated. The streams enter through storm drains - two very large ones at the head end, in particular -- cascading across rocks at low tide and into the Sound.
It's hard to define what a natural shoreline is along such an artificial body of water, but the current banks are probably higher and steeper than they were before the waterway was dredged and the adjacent land was filled. In recent years, there have been some efforts to soften the edges a little bit - for habitat, for recreation, for aesthetic variety.
Beaches have been built near the mouth of the Foss where wave action is higher -- without waves, beaches become something else. These include the tightly constrained gravel pocket beach at Thea's Park and the north-facing beach along the Olympic View shoreline to the east.
On the west side of the Foss, where most of the recent redevelopment has occurred, there have been attempts to build narrow benches into the steep bank, often just below the seawall at the edge of the promenade. These benches become narrow strips of marsh, perched atop walls made from rows of logs and large boulders. I can't speak to how much biological value these features add, but they certainly appear more diverse and more interesting than the uniformly rocked banks typically found in such situations.
Figuring out how to do this offers some interesting possibilities for enhancing the inside edges of marinas (which for all practical purposes, the southern part of the Foss Waterway is), but some design issues need be worked on. For example, perching boulders atop the steep slopes looks like a challenge, since in several places they have toppled, leaving a ragged sheet of geotextile.
More pictures at hshipman: Tacoma