Boise River Report Card
The Boise River is one of the Treasure Valley’s most critical natural resources. What was once used as a dump site for industries, now is the lifeblood for recreation, wildlife, agriculture, and local communities. The Idaho Department of Environmental Quality has designated several beneficial uses for the river section that runs through the heart of Boise. These include our drinking water supply, recreation, habitat for cold water aquatic organisms, and the potential to support salmonid spawning. Unfortunately, however, the impacts to the river’s water quality makes it so some of these beneficial uses are not fully supported.
Navigate the Report
History | Urban River Stewards | Water Quality Tests
Tests: Temperature | pH | Turbidity | Total Coliform Bacteria | Dissolved Oxygen | BOD | Nitrogen | Phosphorus
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The Boise River created a valley that has drawn in humans for thousands of years. Originally, the river was an important area for fishing, hunting, gathering, and harvesting for the indigenous people. Many tribes, including the Shoshone, Bannock, Northern Paiute, and Nez Perce, used the river as a rendezvous spot for trading.
When white settlers took over the valley in the mid-19th century, the tribes were forcibly displaced from the area and the landscape started to change. Most early settlements developed on the northern side of the river to avoid flooding. From 1908-1955, Anderson Ranch, Arrowrock, Lucky Peak, and Diversion dams were built for flood control and irrigation. This turned the Boise River from a wild, free-flowing, and flood-prone river into a managed river system. While the dams have enabled urban growth and made it possible to farm in a high-desert climate, they have also simplified the river’s natural flow, draining many wetlands and causing significant habitat loss for native plant and animal species.
Between the 1940s-1960s, the Boise River was not valued like it is today. It was heavily polluted and being used as a disposal site for garbage, sewage, and animal waste. The water quality was so poor that fish were becoming contaminated with toxins and were unsafe to eat.
Things began to improve after the Clean Water Act passed in 1972, which set limits on the pollution allowed to enter the river and required the removal of accumulated debris and toxic sludge. By 1975, the first segment of the Boise River Greenbelt was built, and the river was on its way to becoming one of the most treasured resources in the valley once again.
Over time, water quality in the Boise river has drastically improved. However, the increase in population growth and development along the river will continue to bring challenges in protecting the health of the Boise River.
Urban River Stewards
Blurb from Lindsey. Include link to the URS page.
Water Quality Tests
Idaho Rivers United’s Urban River Stewards collected water-quality samples from three pre-determined locations along the river from June 2025 to November 2025:
Site #1: Americana Bridge (43.6149, -116.22167)
Site #2: Parkcenter Boat Ramp (43.59507, -116.17472)
Site #3 Barber Park (above the float season put-in) (43.56621, -116.13346)
*Note, that no water quality surveys were recorded in the month of August due to this program being self-led; stewards are able to conduct surveys when it best suits their schedule. This summary highlights how healthy the river is and what conditions looked like during the 2025 sampling season.
A total of 103 water quality surveys were conducted across the three locations. In each survey, Urban River Stewards collected data on the river’s temperature, dissolved oxygen levels, Biochemical oxygen demand, pH, nitrate levels, phosphate levels, turbidity, and the presence of total coliform bacteria.
The Tests
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Temperature affects almost everything in a river. Each species—whether trout, mussels, or aquatic insects—has a temperature range it’s comfortable in. The section of the Boise river that runs through Boise supports cold water aquatic life and salmonid spawning, so it is imperative that river temperatures remain below 22 degrees Celsius.
If water is too warm, fish may become stressed, eat less, or fail to reproduce. Warm water also holds less oxygen, which can lead to low DO levels.
Warmer temperatures can increase the growth of bacteria and algae, sometimes triggering harmful algal blooms.
If water gets colder than normal, it can also shock species or slow their growth.
Temperature changes often come from loss of shade along riverbanks, stormwater runoff from hot pavement, or releases of warm water from industrial or water-treatment facilities.
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pH measures the activity of hydrogen ions in a water sample, meaning it shows how acidic or alkaline the water is on a scale from 0 to 14:
7 = neutral
Below 7 = acidic
Above 7 = alkaline
Most aquatic life thrives when the pH is between 6.5 and 8. Water outside this range can cause stress or even be deadly.
Different pH levels change how nutrients and metals behave in the water.
Low pH (more acidic) can dissolve harmful metals, making them more toxic to fish and people.
High pH can damage fish gills, skin, and eyes, reduce reproduction, and lower overall species diversity.
Changes in pH can come from acid rain, industrial runoff, wastewater, or even natural geology and soils.
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Turbidity is a measure of how clear the water is. In short, the clearer the water, the better. Water that is cloudy or muddy water has high turbidity.
High turbidity can:
block sunlight, reducing plant growth and oxygen production
clog fish gills, making it harder for them to breathe
bury fish eggs or the habitat of insects that fish depend on
increase water temperature because muddy water absorbs more heat
often appear alongside other problems like low DO and higher pollution levels
Common causes of increased turbidity include soil erosion, stormwater runoff, construction, algae growth, and disturbances from boats or livestock.
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Total coliforms are a large group of bacteria commonly found in soil, plants, and surface water, as well as in the digestive systems of people and animals. While most of these bacteria are harmless, there are fecal coliforms, such as E.Coli, that can be harmful to humans and animals if they contaminate our waterways. We test for them because they act like warning lights: their presence can suggest that conditions exist that might also allow harmful germs to survive in the water.
The tests our stewards used simply show whether total coliform bacteria are present or not. These tests do not show the level of contamination or what kind of coliform bacteria is present. Still, if total coliforms show up often or at high levels, it may indicate that the water has been exposed to runoff, waste, or decaying material. This could mean the water is less safe for activities like swimming, and it may stress aquatic species that rely on clean, oxygen-rich water.
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Just like people need oxygen to breathe, fish, insects, and other aquatic animals need oxygen dissolved in the water. Dissolved Oxygen (DO) mainly comes from two sources:
air mixing into the water, especially in fast-moving or turbulent areas (one of the reasons IRU wants more free-flowing rivers: more whitewater = more oxygen)
aquatic plants releasing oxygen during the day
Healthy rivers will have DO levels between 5–6 parts per million (ppm) or higher. When DO levels drop too low, fish and other aquatic organisms can become stressed, struggle to feed, or even suffocate.
Things that can lower DO include:
warm water, which simply can’t hold as much oxygen as cold water
pollution, especially sewage or decaying leaves and algae
algal blooms, which use up oxygen when they die and decompose
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Biochemical Oxygen Demand (BOD) measures how much oxygen is being used by bacteria as they break down organic material such as dead plants, sewage, or runoff from farms. Think of BOD as a “competition meter” between bacteria and aquatic animals:
High BOD means bacteria are using a lot of oxygen, leaving less for fish and insects.
Low BOD means the water is relatively clean and oxygen is more available for wildlife.
When BOD is high, DO levels often drop, which can suffocate oxygen-sensitive species. High BOD is usually a sign of organic pollution, such as untreated wastewater, livestock runoff, or large amounts of decaying vegetation. In slow-moving waters, dissolved oxygen is often consumed by bacteria rather, leaving little left for other aquatic organisms.
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Phosphorus occurs naturally in our rivers and is a nutrient that fertilizes aquatic plants in small concentrations. The tests the stewards conducted measured the phosphate levels in the Boise river. Phosphate is the most commonly used form of phosphorus by biological organisms, as it is utilized to help form DNA, cellular energy, and cell walls. However, phosphate levels that are higher than 0.03 ppm can result in poor water quality conditions.
High levels of phosphorus can lead to:
Excess phosphorus can cause algae to grow rapidly, leading to algal blooms.
When these blooms die, they use up dissolved oxygen, which can suffocate fish and other organisms.
Some algae can produce toxins harmful to wildlife, pets, and people.
Phosphate can enter the water through runoff of fertilizers, wastewater, detergents, soil erosion, and decaying organic matter.
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Like phosphorus, nitrogen occurs naturally in our rivers and is a nutrient that fertilizes aquatic plants. However, if concentration levels are too high it can lead to excessive plant and algae growth, resulting in poor water quality conditions. Nitrogen can appear in several forms, including nitrate, nitrite, and ammonia. The tests the stewards conducted focused on the nitrate levels in the Boise River.
Waters with less than 4 ppm of nitrate are generally considered unpolluted and helps support healthy plant communities. At high levels, it can:
fuel algal blooms that reduce oxygen
be toxic to fish, especially ammonia
make drinking water unsafe
Nitrogen can enter our waterways from sources such as fertilizers, sewage, manure, stormwater runoff, and decomposition of organic matter (for example: fallen leaves that decompose in the river).
Temperature
Temperature affects almost everything in a river. Each species—whether trout, mussels, or aquatic insects—has a temperature range it’s comfortable in. The section of the Boise river that runs through Boise supports cold water aquatic life and salmonid spawning, so it is imperative that river temperatures remain below 22 degrees Celsius.
If water is too warm, fish may become stressed, eat less, or fail to reproduce. Warm water also holds less oxygen, which can lead to low DO levels.
Warmer temperatures can increase the growth of bacteria and algae, sometimes triggering harmful algal blooms.
If water gets colder than normal, it can also shock species or slow their growth.
Temperature changes often come from loss of shade along riverbanks, stormwater runoff from hot pavement, or releases of warm water from industrial or water-treatment facilities.
pH Level
pH measures the activity of hydrogen ions in a water sample, meaning it shows how acidic or alkaline the water is on a scale from 0 to 14:
7 = neutral
Below 7 = acidic
Above 7 = alkaline
Most aquatic life thrives when the pH is between 6.5 and 8. Water outside this range can cause stress or even be deadly.
Different pH levels change how nutrients and metals behave in the water.
Low pH (more acidic) can dissolve harmful metals, making them more toxic to fish and people.
High pH can damage fish gills, skin, and eyes, reduce reproduction, and lower overall species diversity.
Changes in pH can come from acid rain, industrial runoff, wastewater, or even natural geology and soils.
Turbidity
Turbidity is a measure of how clear the water is. In short, the clearer the water, the better. Water that is cloudy or muddy water has high turbidity.
High turbidity can:
block sunlight, reducing plant growth and oxygen production
clog fish gills, making it harder for them to breathe
bury fish eggs or the habitat of insects that fish depend on
increase water temperature because muddy water absorbs more heat
often appear alongside other problems like low DO and higher pollution levels
Common causes of increased turbidity include soil erosion, stormwater runoff, construction, algae growth, and disturbances from boats or livestock.
Total Coliform Bacteria
Total coliforms are a large group of bacteria commonly found in soil, plants, and surface water, as well as in the digestive systems of people and animals. While most of these bacteria are harmless, there are fecal coliforms, such as E.Coli, that can be harmful to humans and animals if they contaminate our waterways. We test for them because they act like warning lights: their presence can suggest that conditions exist that might also allow harmful germs to survive in the water.
The tests our stewards used simply show whether total coliform bacteria are present or not. The tests do not show the level of contamination or what kind of coliform bacteria is present. Still, if total coliforms show up often or at high levels, it may indicate that the water has been exposed to runoff, waste, or decaying material. This could mean the water is less safe for activities like swimming, and it may stress aquatic species that rely on clean, oxygen-rich water.
Dissolved Oxygen
Just like people need oxygen to breathe, fish, insects, and other aquatic animals need oxygen dissolved in the water. Dissolved Oxygen (DO) mainly comes from two sources:
air mixing into the water, especially in fast-moving or turbulent areas (one of the reasons IRU wants more free-flowing rivers: more whitewater = more oxygen)
aquatic plants releasing oxygen during the day
Healthy rivers will have DO levels between 5–6 parts per million (ppm) or higher. When DO levels drop too low, fish and other aquatic organisms can become stressed, struggle to feed, or even suffocate.
Things that can lower DO include:
warm water, which simply can’t hold as much oxygen as cold water
pollution, especially sewage or decaying leaves and algae
algal blooms, which use up oxygen when they die and decompose
Biochemical Oxygen Demand
Biochemical Oxygen Demand (BOD) measures how much oxygen is being used by bacteria as they break down organic material such as dead plants, sewage, or runoff from farms. Think of BOD as a “competition meter” between bacteria and aquatic animals:
High BOD means bacteria are using a lot of oxygen, leaving less for fish and insects.
Low BOD means the water is relatively clean and oxygen is more available for wildlife.
When BOD is high, DO levels often drop, which can suffocate oxygen-sensitive species. High BOD is usually a sign of organic pollution, such as untreated wastewater, livestock runoff, or large amounts of decaying vegetation. In slow-moving waters, dissolved oxygen is often consumed by bacteria rather, leaving little left for other aquatic organisms.
Nitrogen
Like phosphorus, nitrogen occurs naturally in our rivers and is a nutrient that fertilizes aquatic plants. However, if concentration levels are too high it can lead to excessive plant and algae growth, resulting in poor water quality conditions. Nitrogen can appear in several forms, including nitrate, nitrite, and ammonia. The tests the stewards conducted focused on the nitrate levels in the Boise River.
Waters with less than 4 ppm of nitrate are generally considered unpolluted and helps support healthy plant communities. At high levels, it can:
fuel algal blooms that reduce oxygen
be toxic to fish, especially ammonia
make drinking water unsafe
Nitrogen can enter our waterways from sources such as fertilizers, sewage, manure, stormwater runoff, and decomposition of organic matter (for example: fallen leaves that decompose in the river).
Phosphorus
Phosphorus occurs naturally in our rivers and is a nutrient that fertilizes aquatic plants in small concentrations. The tests the stewards conducted measured the phosphate levels in the Boise river. Phosphate is the most commonly used form of phosphorus by biological organisms, as it is utilized to help form DNA, cellular energy, and cell walls. However, phosphate levels that are higher than 0.03 ppm can result in poor water quality conditions.
High levels of phosphorus can lead to:
Excess phosphorus can cause algae to grow rapidly, leading to algal blooms.
When these blooms die, they use up dissolved oxygen, which can suffocate fish and other organisms.
Some algae can produce toxins harmful to wildlife, pets, and people.
Phosphate can enter the water through runoff of fertilizers, wastewater, detergents, soil erosion, and decaying organic matter.