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The City of Portland, Oregon

Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Ave, Suite 613, Portland, OR 97204

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What We Measure

Four important factors of watershed healthList of Watershed Health Indicators

Below is a description of the indicators currently used to calculate the Watershed Health Index and a brief description of their connections to watershed health. These indicators are things that we can measure that tell us about broader environmental conditions. Environmental Services analyzes data and calculates scores for each indicator. 

More information about the methodology behind the calculations of the Watershed Health Index is available in the Technical Memorandum, available on request.


Hydrology is the flow of water over land, underground, and in rivers and streams. Development, dams and culverts all affect hydrology. Environmental Services uses the following two indicators to inexpensively and consistently measure hydrology across watersheds.

Effective impervious area (EIA) is a hard land surface (like a street or roof) that sheds stormwater directly into a water body or a storm drain without detention or infiltration into the ground.

EIA creates higher runoff volume and speed that can cause erosion and flooding, destroy habitat, flush biological communities out of the system, and wash pollutants into rivers and streams.

City stormwater projects and the Stormwater Management Manual reduce EIA to help the city meet Oregon Department of Environmental Quality (DEQ) requirements.


Stream Connectivity
Stream connectivity is a measure of how much of a stream flows freely and how much of it flows through a pipe, culvert or other physical structure.

Pipes confine and concentrate stream flows, which causes flooding and sedimentation upstream. Downstream, increased flow velocities can cause erosion, destroy habitat, and flush aquatic insects out of the system.

This indicator is not used along the main stem Willamette River since there are no dams, culverts or other physical structures that confine or concentrate flows in the city.



Many organizations and government agencies throughout the Willamette basin monitor water quality for a variety of purposes. In Portland, water quality monitoring supports a broad set of responsibilities including watershed protection, wastewater treatment, stormwater management, and sewer construction and maintenance.

Ammonia-nitrogen is the amount of inorganic, dissolved ammonia in water measured in milligrams per liter (mg/L).

Sources include sewage, fertilizers, animal waste, and some industrial uses. Ammonia-nitrogen dissolved in water can stunt aquatic species growth and damage gills. It’s even more harmful when pH and water temperatures increase.


Dissolved copper

Dissolved copper is the fraction of copper remaining in a water sample after filtration and is measured in micrograms per liter (µg/L).

Sources include household plumbing, hull paint on boats, and automotive brakes.

Dissolved copper is toxic to aquatic species and can cause decreased growth, changes in olfactory response, and cell or organ damage.


Dissolved oxygen
Dissolved oxygen (DO) is the amount of oxygen dissolved in water measured in milligrams per liter (mg/L).

All aquatic species need dissolved oxygen during all life stages. Nutrients and organic matter in water, especially when water temperatures are high, can reduce dissolved oxygen levels.


e. Coli
E. coli
bacteria in water is measured by the number of organisms in 100 milliliters of water.

 E. coli indicates the presence of fecal matter from humans and animals. Some kinds of E. coli can cause serious illness in humans. 


Temperature is measured in degrees Celsius. Low summer stream flow and impoundments, such as ponds, can increase stream temperatures.

Temperature influences dissolved oxygen and ammonia-nitrogen concentrations in streams. That impacts the spawning, rearing, feeding, and migration behavior of salmon and other aquatic species. 


Total Mercury
Total mercury is inorganic and organic mercury in water measured as micrograms per liter (µg/L).

Most of the mercury in water comes from atmospheric pollutants that settle on the ground and are washed into rivers and streams by stormwater runoff or erosion. Mercury sources include incinerators, crematoriums, metal smelting and refining, cement kilns, coal-fired power plants, and forest fires.

Mercury accumulates in fish tissues and can impact human health through consumption, so is primarily a concern in waterways where people fish for food. It can also impact wildlife. More research is underway in Portland to understand the contribution of global and local sources and what we can do to reduce the input to our streams.


Total phosphorus

Total phosphorus (TP) is the mass of phosphorus in water and measured in milligrams per liter (mg/L). Phosphorous occurs naturally in streams at low concentrations. Streams in urban or agricultural areas often have higher concentrations that primarily come from fertilizers and other chemicals.

Phosphorus can cause excessive algal growth, which increases pH and decreases dissolved oxygen in streams and adversely impacts the health of aquatic species.


Total suspended solids
Total suspended solids are particles suspended in water measured in milligrams per liter (mg/L). Materials like silt, decaying plants, industrial waste, and sewage contribute to TSS. Metals, pesticides and other nutrients and contaminants adhere to sediment particles.

Suspended solids can cover gravels and smother fry in salmon spawning grounds, affect feeding behavior and clog gills. TSS also blocks sunlight and may decrease food sources for aquatic species.

Sources of TSS include untreated runoff from impervious surfaces (primarily roadways) and erosion of stream bed and banks.


The following indicators measure physical attributes that influence availability of food for aquatic organisms. These habitat features also provide many other benefits including supporting water quality and community livability.

Bank condition
Bank condition is a measure of the percentage of stream bank that has been artificially hardened by riprap, seawalls, or other structures.

Rivers and streams are dynamic and change form in response to changes in flow. Structures that confine a stream prevent it from adapting to variable flows, hinder interaction of a river with its floodplain, reduce in-stream habitat complexity, increase water velocity, and degrade stream structure.


Floodplain condition
Floodplain condition is the percentage of a floodplain covered with vegetation.

Floodplains provide fish and wildlife refuge, store flood waters, and reduce downstream flooding. This measure applies primarily to the Willamette main stem, Columbia Slough and Johnson Creek because these watersheds have topography and hydrology that support significant floodplain development.


Large Wood
Large wood is a measure of the number of large wood pieces within a stream.

In-stream large wood creates pools, stores sediment and organic matter, and maintains stream complexity, and provides refuge and food for salmon.

On the main stem Willamette River, the supply of large wood today is a small fraction of what it once was. There was a recent inventory of large wood on the main stem Willamette but it is not systematically measured. Monitoring protocol and benchmarks have not yet been established.


Riparian integrity
Riparian integrity is a measure of vegetation cover, including trees, within 300 feet of a stream.

Riparian areas shade and cool streams, provide overhead cover, filter sediments and runoff, and provide food for aquatic species. Riparian areas are also a source of large wood in channels, control stream bank erosion and reduce sediment production.  


Shallow water refugia (Willamette River mainstem only)

Shallow water refugia is a measure of any length of stream that is less than 20 feet deep.

Shallow water in large rivers provides rearing habitat and refuge from predators for juvenile salmon. A lack of shallow water habitat in large rivers limits salmon productivity. River dredging and channelization have reduced the amount of shallow water habitat.

This indicator applies only in the Willamette River mainstem. The amount of cool, deep habitat is important in Willamette tributaries.


Stream accessibility
Stream accessibility is a measure of stream miles accessible by juvenile and adult salmon and steelhead.

Culverts, dams, weirs and other in-stream structures create barriers for salmon migrating to the different habitats they use throughout their life cycle.


Substrate Composition
Substrate composition is a measure of the fine sediment and gravel in a stream.

Salmon need gravels and small cobbles for spawning and incubation. The aquatic insects that form the base of stream food webs live in gravel. Fine sediment harms aquatic insects, incubating salmon eggs and fry, and juvenile salmon. In the mainstem Willamette River, shallow water refugia is a better measure for salmon productivity.


Tree canopy
Tree canopy is a measure of tree foliage covering an area.

Trees provide wildlife habitat, reduce stormwater runoff, cool air and water, and are a food source for fish and wildlife. The City of Portland has adopted local goals to increase tree canopy coverage in the Portland Plan, Portland Urban Forestry Plan, Climate Action Plan, and other plans and policies. 



The presence, abundance, and interactions of aquatic, riparian, and terrestrial species give a picture of overall watershed health. Fish, macroinvertebrates and birds are sensitive “canaries in the coal mine.” Data about them can help the city identify trends in water quality and issues that might become bigger problems if not addressed. Some species are also protected under the Endangered Species Act or are at risk of becoming threatened or endangered.

Birds are indicators of the health of biological communities and overall watershed conditions.

The Bird Integrity Index (BII) measures avian community health to determine the health of larger riparian areas. This index, designed specifically for use in Portland, takes into account the presence of native or non-native species, migratory patterns, foraging and nesting, and other factors.

The score for this indicator is still under development for the main stem Willamette River, since the data scale and models for a large river system are different from what we use for smaller streams. 



The health of Portland’s streams is related to the abundance, productivity, distribution, and diversity of fish populations, especially salmon.

For the Watershed Health Index, Environmental Services assesses fish population health using the Index of biotic Integrity (IBI). The IBI measures fish species richness and composition, number and abundance of indicator species, reproductive behavior, and condition of individual fish.

The score for this indicator is still under development for the main stem Willamette River, since the data scale and models for a large river system are different from what we use for smaller streams.


Aquatic macroinvertebrates live in water all or part of their lives, have no backbone, and are visible to the naked eye. Examples include freshwater mussels, mayflies, stoneflies, and other bottom-dwelling critters. They process organic matter and are an important food source for fish, birds and other wildlife. Macroinvertebrates are good indicators of watershed health because they are sensitive to biological conditions of a stream.

The Oregon Department of Environmental Quality developed the PREDictive Assessment Tool for Oregon (PREDATOR) to measure aquatic insects, specifically macroinvertebrates.

The scores for this indicator are not applicable for the main stem Willamette River and Columbia Slough, since the data and models for macroinvertebrates are not effective measures of watershed health for larger, slower-moving, water bodies