Oregon Water Quality Index Report for Upper Willamette Basin 

Water Years 1986-1995

For illustrative purposes, the Willamette Basin is separated into three parts: Upper Willamette, Middle Willamette, and Lower Willamette. The Upper Willamette includes the headwaters of the Coast and Middle Forks of the Willamette River, the McKenzie subbasin, and the mainstem Willamette River from the convergence of the forks to the point immediately upstream of the convergence with the Santiam River. The Middle Willamette extends to the Willamette River at Canby and includes the North and South Santiam, Yamhill, and Molalla-Pudding subbasins. The Lower Willamette extends to the mouth of the Willamette River and includes the Tualatin and Clackamas subbasins.

Significant trends in the Upper Willamette Basin show improvement in water quality. Comparing minimum seasonal Oregon Water Quality Index (OWQI) values (Table 1), water quality in the Upper Willamette basin ranges from excellent (Middle Fork Willamette River site) to poor (Calapooia River site). Water quality data were routinely collected by the DEQ Laboratory in 1986-1995. Special intensive studies were performed in the Coast Fork Willamette Subbasin in 1987-1992.

Water quality is commonly impacted by the introduction of organic matter to streams. The presence of organic matter increases biochemical oxygen demand, which means less dissolved oxygen is available for aquatic life. The introduction of untreated animal or human waste increases the possibility of bacterial contamination of water, increasing the risk of infection to swimmers. Eutrophication is the process of enrichment of water with nutrients, mainly nitrogen and phosphorous compounds, which results in excessive growth of algae and nuisance aquatic plants. It increases the amount of organic matter in the water and also increases pollution as this matter grows and then decays. Employing the process of photosynthesis for growth, algae and aquatic plants consume carbon dioxide (thus raising pH) and produce an overabundance of oxygen. At night the algae and plants respire, depleting available dissolved oxygen. This results in large variations in water quality conditions that can be harmful to other aquatic life. While natural sources of nutrients can influence eutrophication, the introduction of nutrients strengthens the process. Sources of nutrients include wastewater treatment facility discharge and faulty septic systems, runoff from animal husbandry, fertilizer application, urban sources, and erosion. High water temperatures compound the decline in water quality by causing more oxygen to leave the water and by increasing the rate of eutrophication. Removal of streamside vegetation, among other factors, influences high stream temperature and, via erosion, increases sedimentation of streams.

Table 1. Seasonal Average OWQI Results for the Upper Willamette Basin (WY 1986 -1995)

Summer: June - September; FWS ( Fall, Winter, & Spring): October - May
Scores - Very Poor: 0-59, Poor: 60-79, Fair: 80-84, Good: 85-89, Excellent: 90-100

Coast Fork Willamette Subbasin

The Coast Fork Willamette subbasin was intensely studied in 1987-1992. DEQ Laboratories continues to routinely monitor the Coast Fork Willamette River at Mt. Pisgah Park. A variety of point and non-point sources of pollution were noted, including agriculture and logging operations, municipal sewage treatment plants (STPs), landfills, and confined animal feeding operations.

The most upstream monitoring site in the Willamette basin is the Coast Fork Willamette River upstream of Cottage Grove at Highway 99. Water quality was impacted by high levels of fecal coliforms, biochemical oxygen demand, and total phosphates. The greatest impacts occurred during summer low flow conditions, although water quality impacts were also associated with heavy precipitation. This indicates the introduction of organic materials to the water. High levels of fecal coliform can be associated with untreated human or animal waste. The combination of organic material and high water temperatures during the summer increase biological and chemical activity. This site is directly downstream of log ponds associated with upstream logging operations. Agricultural operations also impact water quality here. Water quality at the Coast Fork Willamette River upstream of Cottage Grove ranges from fair in the summer to good during the fall, winter, and spring (Table 1).

The monitoring site on Row River at County Road is located five miles downstream of Dorena Dam. Water quality impacts are minor and occur during low flow conditions. Relatively high levels of biochemical oxygen demand and total phosphates are accompanied with high temperatures. This stretch of Row River exhibited excellent general water quality throughout the year (Table 1).

The Coast Fork Willamette River at Creswell was impacted by high levels of fecal coliform during low flow conditions. In addition to sources noted above, the Cottage Grove STP may have contributed to adverse water quality conditions. Eutrophication was evidenced at this site by high temperature, dissolved oxygen supersaturation, and high pH. As a result, OWQI values were fair in the summer on the average (Table 1). During the fall, winter, and spring, high flows maintained excellent water quality (Table 1).

The most downstream site on the Coast Fork Willamette River is at Mount Pisgah Park. This stretch of river is the recipient of all accumulated upstream sources not removed by natural self-purification, including nursery operations immediately upstream. High levels of fecal coliforms, total phosphates, biochemical oxygen demand, and ammonia and nitrate nitrogens impacted water quality primarily during fall, winter, and spring. These constituents are occasionally present during summer low flow conditions. High water temperatures and eutrophication is evident at this site during summer months. As a result, high pH values, high dissolved oxygen levels, and high biochemical oxygen demand impair water quality. On the average, water quality is good throughout the year (Table 1).

In comparing OWQI values from the most upstream to most downstream of Coast Fork Willamette River sites, it is interesting to note that water quality remains relatively steady throughout the river in the fall, winter, and spring. Water quality improves from upstream to downstream during the summer months. This indicates diminishing sources of pollution towards the mouth of the river.

Middle Fork Willamette Subbasin

The Middle Fork Willamette Subbasin has more flow controlling reservoirs than any other subbasin in the Willamette Basin. Though presenting a barrier to fish passage, the system of dams and reservoirs maintains relatively high flows and low temperatures throughout the year, compared to the Coast Fork Willamette River. The Middle Fork Willamette River at Jasper is occasionally impacted by high levels of total phosphates and biochemical oxygen demand during heavy precipitation. This indicates pollution from run-off, which is present in any river system. This site ranks third in quality compared to all Oregon streams routinely monitored by DEQ Laboratories. Water quality is consistently excellent throughout the year (Table 1).

McKenzie Subbasin

Like the Middle Fork Willamette River, the McKenzie River has consistently excellent water quality throughout the year (Table 1). Because the monitoring site on the McKenzie River at Coburg Road is downstream of suburban and industrial areas, OWQI values are slightly less than for the Middle Fork Willamette River at Jasper. High levels of biochemical oxygen demand and total phosphates impacted water quality during summer low flow conditions in the late 1980's. These impacts lessened in severity over time, so a significantly increasing trend in water quality was seen during water years 1986 to 1995 (Figure 1). This increase is probably a result of increasing summer flows.

Figure 1. Trend Analysis Results for the McKenzie River at Coburg Road

Upper Willamette Subbasin

Upper Willamette Subbasin water quality is primarily influenced by extensive agriculture, although municipal and industrial point sources and urban non-point sources contribute to water quality conditions as well.

The most upstream site on the mainstem Willamette River is at Oregon Highway 126 in Springfield. This site is about two miles downstream of the confluence of the Coast and Middle Forks of the Willamette River. Water quality variation at this site is dependent on water quality in the Coast Fork Willamette River, with dilution provided from the Middle Fork Willamette River. Water quality at this site is also influenced by Mill Creek, a small tributary adjacent to the monitoring site. Mill Creek drains an industrial area in the City of Springfield. Water quality is occasionally impacted during high and low flows by increases in total phosphates and biochemical oxygen demand, accompanied by high concentrations of total solids and fecal coliforms. OWQI results indicate the Willamette River at Springfield is consistently excellent (Table 1).

After flowing through Springfield and Eugene and receiving the McKenzie River, the Willamette River becomes a braided stream that meanders northerly through the Grand Prairie. Water quality in the Willamette River at Highway 99E in Harrisburg is generally good throughout the year (Table 1). Non-point source pollution is evident, as relatively high levels of total phosphates and biochemical oxygen demand indicate runoff containing organic materials enters the river during the fall, winter, and spring. Occasionally, high levels of total solids and fecal coliforms are present during this time. Summer low flow conditions with high water temperatures stimulate the process of eutrophication. High dissolved oxygen supersaturation and high concentrations of biochemical oxygen demand reflect the occurrence of eutrophication in this stretch of the Willamette River.

Long Tom River enters the Willamette River approximately twelve miles downstream of the monitoring site in Harrisburg. Long Tom River drains the Coast Range west of Eugene and Junction City. Logging uses dominate the upper reaches of Long Tom River. The river is impounded at Fern Ridge Lake before it is allowed to meander through the mostly agricultural Grand Prairie. The Monroe STP is situated about two miles upstream of the monitoring site on the Long Tom River at Stow Pit Road. Water quality is most frequently impacted during the fall, winter, and spring, when high concentrations of fecal coliforms, total phosphates, nitrate and ammonia nitrogens, total solids, and biochemical oxygen demand are present. This indicates the presence of untreated human or animal waste and other organic material in the river. These wastes enter the river as a result of runoff and erosion associated with precipitation and high river levels. Occasional STP overflows may occur during periods of heavy precipitation. During low flow summer months, high temperatures and high concentrations of total phosphates and nitrate and ammonia nitrogens influence eutrophication in the Long Tom River. High pH, high dissolved oxygen supersaturation, and high biochemical oxygen demand are the results of this process. OWQI values are generally poor throughout the year (Table 1).

Marys River enters the Willamette River approximately seventeen miles downstream of its confluence with Long Tom River. Marys River drains the Coast Range west and south of Corvallis. Logging uses dominate the drainage. The Philomath STP is situated about eleven miles upstream of the monitoring site on Marys River at Highway 99W in Corvallis. In the fall, winter, and spring, high concentrations of fecal coliforms, total phosphates, total solids, biochemical oxygen demand, and nitrate nitrogens impact water quality. This indicates the presence of untreated human or animal waste, nutrients, and other organic materials in the water. These wastes enter the river as a result of runoff and erosion associated with precipitation and high river levels. Occasional STP overflows may occur during periods of heavy precipitation. These conditions persist in the summer, when high water temperatures are added to the list of concern. OWQI values are generally poor during fall, winter, and spring and fair during the summer (Table 1). During the last ten years, Philomath STP facilities were improved and the severity and frequency of water quality impacts to Marys River have lessened. Trend analysis shows a significant improvement in water quality during this time (Figure 2).

Figure 2. Trend Analysis Results for Marys River at Corvallis

The monitoring site on the Willamette River at Oregon Highway 34 in Corvallis is approximately one mile downstream of the confluence with Marys River. Water quality is impacted more frequently in the fall, winter, and spring than in the summer. Wet weather impacts include high levels of fecal coliforms, total phosphates, nitrate and ammonia nitrogens, total solids, and biochemical oxygen demand. Summer impacts include high temperature, nitrate nitrogen, and total solids. These impacts are most likely the result of urban and agricultural non-point source pollution, for example run-off and storm drain discharge. Water quality is good throughout the year (Table 1). During the last ten years, the severity and frequency of water quality impacts to the Willamette River at Corvallis have lessened. STP effluents have improved in quality as a result of the addition of secondary treatment to STP's in the region. Industrial point sources have been removed or improved. Trend analysis shows a significant improvement in water quality during this time (Figure 3).

Figure 3. Trend Analysis Results for Willamette River at Corvallis

Calapooia River enters the Willamette River approximately eleven miles downstream from the Willamette River monitoring site in Corvallis. The Calapooia River's headwaters drain the Western Cascades and the primary land use in the upper portion of the watershed is logging. The lower thirty-five river miles are used for extensive agriculture. DEQ Laboratory monitors the Calapooia River at Queens Road in Albany. There are no known significant point sources of pollution affecting water quality at this monitoring site. Throughout the year, high levels of nutrients significantly impact water quality in the Calapooia River. Average concentrations of nitrate nitrogen in the Calapooia River were 1.25 mg/L, compared to 0.35 mg/L in the Willamette River at Albany. High concentrations of nitrate and ammonia nitrogen, total phosphates, fecal coliforms, total solids, and biochemical oxygen demand result in poor water quality during the fall, winter, and spring (Table 1). High concentrations of total solids, nitrate and ammonia nitrogens, and total phosphates combine with high water temperatures in the low flow summer months. These conditions influence eutrophication in the river and high levels of dissolved oxygen supersaturation and biochemical oxygen demand arise. Water quality is generally poor in the summer months (Table 1).

After the Willamette River monitoring site in Corvallis, the Willamette River flows twelve miles and receives waters from the Corvallis STP and Calapooia River before reaching the next monitoring site in Albany at Highway 20. The Albany STP and industrial point sources are located downstream of this site. Water quality is impacted most significantly by high levels of total phosphates, mainly in the fall, winter, and spring. High concentrations of fecal coliforms, nitrate and ammonia nitrogens, total solids, and biochemical oxygen also impact water quality at this site. Corvallis STP experiences frequent overflows during storm events. Water quality is generally fair during fall, winter, and spring and good during summer (Table 1). STP effluents have improved in quality as a result of the addition of secondary treatment to STP's in the region. Industrial point sources have been removed or improved. Trend analysis shows a significant improvement in water quality during this time (Figure 4).

Figure 4. Trend Analysis Results for Willamette River at Albany

Acknowledgment: Software used for trend analysis was the WQHydro package developed by Eric Aroner of WQHydro Consulting.

References

Oregon Department of Environmental Quality, Water Quality Division, 1988. 1988 Oregon Statewide Assessment of Nonpoint Sources of Water Pollution. Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1988. Oregon's 1988 Water Quality Status Assessment Report (305(b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1990. Oregon's 1990 Water Quality Status Assessment Report (305(b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1992. Oregon's 1992 Water Quality Status Assessment Report (305(b) Report). Portland, Oregon.

Oregon Department of Environmental Quality, Water Quality Division, 1994. Oregon's 1994 Water Quality Status Assessment Report (305(b) Report). Portland, Oregon.

Written by Curtis Cude, Oregon Department of Environmental Quality, Laboratory Division