An average of 27% of Puget Sound’s natural shoreline is armored by retaining structures, increasing to ~65% near urban centers. These structures are usually composed of vertical seawalls and riprap boulder fields.  
Enhancement features at OSP were incorporated because juvenile salmonids use the Seattle urban nearshore of Puget Sound for rearing and migration, with the nearby Green/Duwamish River being the closest source for both wild and hatchery juvenile salmon.  Juvenile Chinook and chum salmon use nearshore habitats more than other species of salmon.  Improved habitat for Chinook salmon is often a focus for shoreline restoration or enhancement efforts in the region, because Puget Sound Chinook are listed as threatened under the Endangered Species Act.