Watershed Health - 2020

Maintaining Healthy Water Quality 

The Puget Sound region is a unique network of mountain peaks, plateaus, rivers, lakes, and marine wCollecting water samplesaters. These natural wonders make Pierce County a beautiful place to visit, live, work and play. Maintaining healthy water quality in the streams, rivers and lakes that connect the Cascade Mountains to Puget Sound is essential to the quality of life and prosperity of Pierce County residents, businesses and wildlife.

Water quality has declined in most areas of Pierce County as the population and development have grown over the past century. The most common water quality concerns in Pierce County streams are high levels of bacteria, nitrogen and phosphorus, elevated summer temperatures and low dissolved oxygen concentrations.

Water Quality Data 

Our water quality specialists go out in the field monthly to monitor water quality at streams throughout Pierce County. We also collect benthic samples from a subset of streams every summer. Below are 2020 results from our stream monitoring program. This report summarizes results between October 1, 2019, and September 30, 2020.

Measuring water samplesThe Benthic Index of Biotic Integrity (BIBI) score is calculated using benthic macroinvertebrate (bugs living on the bottom of streams) samples. We collect these samples from specific streams every several years with the help of the Pierce Conservation District. Macroinvertebrates are useful indicators of stream quality because they generally spend their life cycles in a small area, have a short life span and are sensitive to subtle changes in water quality or habitat. Different macroinvertebrate species have various levels of tolerance to pollution. Some species that are important food sources for salmon, such as mayflies, stoneflies, and caddis flies, are very intolerant to pollution. In an unhealthy stream the amount of these species will decline while the numbers of more pollution-tolerant species like leeches and black fly larvae, which salmon do not eat, will increase.

The Water Quality Index (WQI) score is calculated using monthly stream water quality sampling for bacteria, pH, dissolved oxygen, temperature, turbidity, total suspended solids, total nitrogen and total phosphorus. It is a measure of eight common parameters that are known to impact the health of freshwater streams. By observing the chemical and physical properties of the stream, we can better understand stream health and the impacts it may have on humans, fish and wildlife.

Watershed health is classified into three categories of concern—low, moderate and high—using BIBI and Water Quality Index scores. 

Click on the pictures below to view larger versions of the graphics.

Water quality health index key
Key Peninsula, Gig Harbor and Islands Watershed WQI
Puyallup Watershed WQI
Nisqually Watershed WQI
The Monitoring Unit (Water Quality Section) helps ensure Pierce County meets the requirements of the National Pollutant Discharge Elimination System (NPDES) Phase I Municipal Stormwater Permit. Pierce County’s monitoring team collects local data to measure whether water quality is getting better or worse and identify patterns in healthy and impaired Puget lowland streams and Puget Sound urban shoreline areas. We also collect data for NPDES driven watershed modeling and Total Maximum Daily Load (TMDL) projects.
Clarks Creek TMDL Project 
The Clarks Creek restoration plan was created to restore water quality and protect the watershed by identifying and prioritizing the treatment of stormwater flow and the reduction of sediment in the creeks of the watershed. The improvement plan is funded through a combination of local dollars and local, state and federal grant monies. A review in 2021 will reassess the plan and potentially recommend changes. You can read more about the Clarks Creek TMDL Project on our project webpage.
Water Level and Weather Data
There are many water level and weather monitoring stations spread throughout Pierce County. Local live weather station data can be found here. Our water quality data portal can be found here.
Shellfish Protection 
Pierce County conducts shellfish beach sampling and coordinates with the Tacoma-Pierce County Health Department and other partners on programs to keep pollutants out of shellfish beds.

Carol Falkenhayn Maloy

Water Quality Supervisor

Phone: (253) 798-2573


7:30 a.m.–4:00 p.m.

Mailing Address:

2702 S 42nd St, Ste 109

Tacoma, WA 98409-7322