Section 1. Introduction

Puget Sound is unique in the lower 48 Unites States because of its fjord-like physiography, inland extent, wide range of depths, and urbanized watersheds and shorelines. Limited exchange of seawater between sub-basins within Puget Sound can result in long residence times, potentially increasing the susceptibility of biota to contamination introduced through human activities. The varied habitats within Puget Sound support multiple life history stages of many species, potentially exposing sensitive life stages to contamination. There are multiple water quality concerns in Puget Sound:

• Levels of toxic contaminants in biota that live or feed in Puget Sound.
• The eutrophication of marine waters, producing hypoxic and anoxic regions.
• Wastewater contamination, principally from combined sewer overflows or septic systems
• Harmful algal blooms, which introduce toxins that enter the food web
• Acidification of marine waters, and the adverse ecological effects that result.

Degradation of water quality in Puget Sound occurs through three primary mechanisms. The first is through the introduction of toxic contaminants, primarily comprising manufactured synthetic chemicals, but also including compounds that occur naturally that are concentrated in the local environment to toxic levels via human activities. The second is through human-caused changes in naturally occurring chemicals, compounds, or physical parameters (e.g., temperature, turbidity, nutrients, pH). The third is through introduction of new diseases or pathogens, or through other activities that cause an unnatural increase in disease organisms.

Here we treat the these first two of these mechanisms, focusing on the marine and estuarine waters of Puget Sound, and restricting our treatment to degradation caused by human activities. Future editions of the Update will expand the treatment to include pathogens, the condition of fresh water systems, and natural sources of change in water quality.