Increasing development across the Puyallup watershed is hurting salmon populations already returning in low numbers. That is a finding in the recently released State of Our Watersheds Report by the treaty tribes in western Washington.
From the report:

Increased population pressure and development, with the conversion of forested areas to impervious surfaces, is the major factor affecting water quality in the region. Greater numbers of people in the region result in greater volumes of waste water, more septic systems and more sources of nutrients entering surface waters. As a result of development, once-forested land has been replaced with buildings, roads and lawns.

In 2015 only about 17,000 juvenile chinook out-migrated from the Puyallup River, a near record low, according to the Puyallup Tribe’s yearly salmon population report.

The report specifically calls out Clarks Creek, an important tributary in the lower watershed and home to two hatcheries owned by the Puyallup Tribe of Indians:

Clarks Creek supports the highest salmon spawning densities of any incorporated area in the watershed. Clarks Creek provides critical habitat for Chinook salmon. Within the creek can also be found coho, chum, cutthroat, and steelhead salmon. Over-growing plants, stormwater runoff pollution, fecal coliform and low levels of dissolved oxygen all plague Clarks Creek. The health of this creek and its sustainability are in jeopardy. Clarks Creek basin saw an increase in impervious surface in all of its watershed analysis units from 2006-2011 and remains degraded or severely damaged.