Water Quality Improvement Project
Henderson Inlet is one of five inlets that form the southern end of Puget
Sound. Woodland and Woodard Creeks are the largest tributaries in the 30,000-acre watershed, draining 80% of the basin. The other major streams in the
watershed: Dobbs Creek (East Creek), Meyer Creek (Snug Creek), and Sleepy Creek
(Libby Creek), drain small areas of the Dickerson Point and Johnson Point
peninsulas (Thurston County PHSS and WWM, 1995).
Water quality issues
We conducted a
water quality study in Henderson Inlet watershed during 2002-2005. The study
evaluated water quality impairments.
Dissolved oxygen and pH issues in freshwater were largely found to be related
to natural causes, such as discharge from groundwater or wetlands. However, some
dissolved oxygen issues appeared to be related to too many nutrients (nitrogen
and phosphorus) from human sources entering the water bodies. Our hydrologic
analysis was not able to explain why the water is too warm in parts of Woodland
Creek, one of the larger tributaries to Henderson Inlet. Other likely human
sources of incoming pollution include failing septic systems, pet waste, and
poor livestock management practices.
The study also found that fecal coliform bacteria concentrations were too
high throughout the watershed. The water quality study found several stormwater
outfalls carrying significant bacteria loads. Stormwater, while not itself a
source of bacteria, contributes to bacteria problems by carrying pollution into
waterways, even from some distance away.
Wildlife, too, can contribute bacteria. Wildlife is generally considered part
of the “natural background.” However, there may be management opportunities to
reduce bacteria where human activities encourage unusual numbers of wildlife:
for instance, waste management in commercial areas, or feeding waterfowl along
What is being done?
The total maximum daily load (TMDL) report was developed and submitted to the
Environmental Protection Agency (EPA) for approval in 2006, after a public
review and comment period. EPA approved it in 2007. The
TMDL report set goals for reducing bacteria at important locations. The
report's implementation strategy made recommendations for reducing nutrients
in the watershed. We sent the final
water quality implementation plan to EPA on July 31, 2008.
Status of the project
We completed water quality sampling for an effectiveness monitoring project
in 2015 to evaluate the progress of water quality cleanup. We finalized the
report summarizing findings in early 2017.
This study found statistically
significant fecal coliform declines across the watershed. Water quality
improvements are largely due to the hard work of local partners.
quality has improved, state standards are still not being met. Cleanup work
needs to continue and includes:
- Improved management
of stormwater discharges.
- Implementation of an on-site septic system
operations and maintenance program.
- Source investigation including septic
surveys, water quality monitoring, and visual surveys of land use and management
- Technical assistance to landowners.
- Informational workshops and
other outreach aimed at encouraging landowners to improve land use practices.
- Oversight of sources with discharge permits.
- Water quality
monitoring to guide cleanup; assess effectiveness of cleanup actions; monitor
progress towards water quality goals; and, ultimately, demonstrate compliance
with water quality standards.
- On-going evaluation, by the technical advisory
group, of the effectiveness of cleanup actions and changes to the cleanup
strategy as needed.
Why this matters
Oxygen dissolved in healthy water is vital for fish and
aquatic life to “breathe” to survive. It is more difficult to transfer
oxygen from water to blood than it is to transfer oxygen from air to
blood. Therefore, it is critical that an adequate amount of oxygen is
maintained in the water for this transfer to take place efficiently and
sustain aquatic life. Oxygen is also necessary to help decompose organic
matter in the water and bottom sediments as well as for other biological
and chemical processes.
Fecal coliform is a type of “bacteria” common in human and animal
waste. It indicates that sewage or manure is entering a water body. As
the level of fecal coliform increases the risk of people getting sick
from playing or working in the water increases. Bacteria can get into
our waters from untreated or partially treated discharges from
wastewater treatment plants, from improperly functioning septic systems,
and from livestock, pets and wildlife.
People can help keep bacteria out of the water. Properly collect, bag, and
trash dog poop. Check your on-site sewage system to make sure it is maintained
and working properly. Ensure livestock and manure are kept away from the water.
pH is a measure of how acidic or alkaline the water is. The pH is
measured on a scale of 0-14, with the lower numbers indicating acidic conditions
and higher numbers alkaline conditions. Optimal pH levels to support fish and
wildlife should range from 6.5 to 9.0. A pH of 7 is neutral.
pH can affect the solubility of nutrients and metal compounds. By affecting
the solubility of nutrients, it can change the amount of nutrients available for
plant growth. If too many nutrients are available, aquatic plants can grow out
of control. When these plants decompose, they can deplete the water of oxygen.
The solubility of many metal compounds also changes greatly with pH. Generally,
a reduction in pH (more acidic) increases the solubility of heavy metals. When
more metals are dissolved in the water, aquatic animals may absorb them faster.
Therefore, a lower pH (more acidic) may make these metals more toxic to aquatic
Water temperature influences what types of organisms can live in a
water body. Cooler water can hold more dissolved oxygen that fish and other
aquatic life need to breathe. Warmer water holds less dissolved oxygen. Many
fish need cold, clean water to survive.
One way to cool water temperature is to shade the water body by adding or
retaining streamside vegetation.
Unless otherwise specified, the following documents are Ecology publications.
Quality Assurance Project Plan: Henderson and Nisqually TMDL Study
Water Quality Improvement Report
Henderson Inlet Watershed FC Bacteria TMDL – Water Quality Implementation Plan
Quality Assurance Project Plan: Henderson Inlet Fecal Coliform
Total Maximum Daily Load Effectiveness Monitoring Study (Water
Quality Study Design)
Henderson Inlet Fecal Coliform Total Maximum Daily Load: Water
Quality Effectiveness Monitoring Report
WRIA 13: Deschutes
Watershed Information (Water web site)
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