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Curlew Lake Cyanobacteria Management Plan (CMP)

Curlew Lake is a large lake located in Ferry County, Washington approximately 10 miles from Republic. With three resorts, a state park, and nearly 600 residents inhabiting the shoreline, Curlew Lake is an important economic and recreational resource to local and touring users. Historically, Curlew Lake has been enjoyed for its clear and cold water but recent increases in aquatic weeds and algae (cyanobacteria) blooms and decreases in water clarity threaten to impede public uses. As such, the Ferry Conservation District (FCD) identified water quality in Curlew Lake as a top priority in 2020 and applied for and received a Washington Department of Ecology Water Quality Algae Control Program grant to develop a cyanobacteria management plan (Herrera, 2023). The first step in designing a plan is the development of a Quality Assurance Project Plan (QAPP) that has to be approved. That plan can be viewed by clicking here. 

The Ferry Conservation District has teamed up with Herrera Environmental Consultants and WSU who have prepared a plan to be used as a guideline and tool for allocating resources to implement management activities for reducing toxic algae blooms and associated impacts at Curlew Lake. The CMP will identify community concerns and set priorities, goals, and objectives,  and will lay out management strategies based on those concerns as well as include a stakeholder involvement plan to educate and gather feedback from the community, and a funding plan describing how funds will be generated for the implementation of management strategies (Herrera, 2023).


Over the course of 2023, the Ferry Conservation District will be taking part in the data and sampling collections.  Three locations on the lake as well as several adjacent watershed locations will be routinely reported on. 


Curlew Lake is a 921-acre lake located in the glacier-carved Curlew Valley in Ferry County, northeastern Washington. The lake is deep with a steep shoreline. Curlew Lake is a natural lake regulated by a shallow dam at its northern outlet. Curlew Lake provides visitors and residents with opportunities for kayaking, boating, fishing, swimming, water skiing, canoeing, and sailing. Public access is available at Curlew Lake State Park at the lake's south end. Historically, Curlew Lake has been enjoyed for its clear and cold water but recent increases in aquatic weeds and algae (cyanobacteria) blooms and decreases in water clarity threaten to impede public uses. As such, the Ferry Conservation District (FCD) identified water quality in Curlew Lake as a top priority in 2020 and applied for and received a Washington Department of Ecology Water Quality Algae Control Program grant to develop a cyanobacteria management plan

Study Areas and Surroundings

Curlew Lake is a steep, deep lake with three deep basins and an adjoining shallow lake, Roberta Lake, to the south connected by a channel with a shallow sill. The Curlew Lake watershed is 65 square miles in Ferry County. The watershed includes Colville National Forest, cattle rangeland, rural residences, and recreational and vacation homes. There are 842 residential parcels in the lakes’ watershed, including 66 homes categorized as “Vacation and Cabin.” Per the 2019 National Land Cover Database (NLCD), the majority of land cover is evergreen forest about one-third is scrub/shrub, and about one percent is categorized as developed. Per the Ferry County parcel database, about 10 percent of the land use is agriculture by area and 14 percent is residential. The remainder is largely categorized as government or commercial forestland or “undeveloped.”
There are four major tributaries to the lake: Trout Creek, Barrett Creek, Mires Creek, and Herron/Roberta Creek. Of these creeks, only Trout Creek flows into the lake throughout the year. The lake serves as the headwaters for Curlew Creek, which ultimately discharges to the Kettle River in the Columba River basin.

History of the Lake

While putting together the Project's Quality Assurance Plan, Herrera dug up some very interesting history of the Curlew Lake area. According to their research, the study area is within the traditional territories of several Native American tribes: the Colville, Sinixt, and Sylix (Okanagan). Twenty-four Native American sites have been located in the vicinity of Curlew Lake (Perry 1982). Intergenerational Native American stories have told that the lake was used by small groups for shellfish harvest along the sandy shorelines (Damman, pers. comm. in Juul et al. 1988).


Fur trading brought the first European settlers to the Ferry County region in the 1820s. In the late 1800s, prospectors came to Ferry County to establish mineral claims, chiefly for gold. In 1872, all of modern Ferry County was set aside as Indian Reservation. In 1892, the north half of Ferry County was opened to homesteading, decreasing the extent of the previously established Indian Reservation. Logging increased through the first half of the 1900s, and the Colville National Forest was established in 1907. Ferry County remained remote and inaccessible until roads and communication systems were built by the Civilian Conservation Corps. Lake Roosevelt was also developed in the 1930s, which spurred employment, electricity, and irrigation. Ferry County particularly the town of Republic, has relied on mining for decades. The Republic mines were the major producers of gold in the state for many years in the 20th century. Active gold mining ceased in 2018, and as of 2022, there are two active sand and gravel operations in the watershed (Hanlon 2022.


Lake Roberta and Curlew Lake were originally two separate lakes. In the early 1900s, a channel was dug between the lakes so logs could be floated north to the Karamin Mill. Except for this channel, the two lakes are separate hydrological entities. In the mid-1930s for example, Lake Roberta dried up during one summer without an equivalent drop in the elevation of Curlew Lake (Juul et al. 1988).


In 1917 the Washington State legislature granted the Curlew Irrigation District the right to overflow the shore lands bordering the lake up to and including the high-water mark. Two years later a recommendation was made by the state game warden in 1919 that Curlew Lake be made into a reservoir for storing irrigation water. In 1926, with the construction of a 3-foot (0.91 m) dam at the north end of the lake, the water level was stabilized at an elevation of 2,333 feet (711 m). In 1984, the wooden dam was removed (Juul et al. 1988).


Today, the primary land use in the study area is timber, ranching, and low-density residential. Curlew State Park was established in 1959 and includes facilities for picnicking, camping, hiking, biking, boating, fishing, and swimming.

Previous Studies

Herrera also prepared a summary of existing data:


Sporadic monitoring of Curlew Lake has occurred since the 1980s. The most intensive monitoring was conducted from 1986 to 1987 through the Washington State Water Resources Center, Washington State University, and the University of Washington (Juul et al. 1988). This study collected a substantial amount of data on lake and stream water quality, hydrology, lake plankton, macrophyte community, and lake sediment. The report’s data has not been digitized and is not incorporated into this summary. Juul et al. (1988) concluded that the lake was mesotrophic (moderately productive) and that resulted from “(1) occasional high water levels flooding near-shore septic systems, (2) livestock grazing adjacent to inlet streams, (3) past timber harvesting practices, and (4) a groundwater source that has a high concentration of phosphorus in some areas.” Juul et al. (1988) recommended the following to preserve and restore water quality: (1) non-point source control (e.g., livestock), (2) harvesting of non-game fish, particularly northern pikeminnow, to remove nutrients, (3) protect and restore wetlands to act as nutrient sinks, (4) construct a dam at the outlet to control lake levels and allow winter drawdowns, and (5) implement and enforce development zoning ordinances. Juul et al. (1988) did not recommend in-lake nutrient management through alum, hypolimnetic aeration, or dredging because of the large cost of those approaches.

In the 1990s, the lake was monitored twice nearly every year, and a more thorough investigation of the lake, its inlets, and its outlet was undertaken in 2010 and 2011. However, a formal report was not prepared for the 2010-2011 study.

There are no discernable long-term trends in the water transparency and surface phosphorus concentration in the lake, but there is limited evidence that phosphorus levels in the hypolimnion have increased (Figures 5 and 6). The data available suggest that Curlew Lake is borderline mesotrophic/eutrophic, and phosphorus levels are substantial in hypolimnion (>100 µg/L). Available profile data show that the lake is strongly stratified in April with a thermocline at approximately 5 meters (Figure 7). Thermal stratification appears to remain strong through October and weakens, but does not disappear, in November. No lake monitoring has occurred between December and March while the lake is partially or completely frozen over. We anticipate that the lake undergoes a brief mixing event in November or December before becoming covered in ice and becoming winter stratified, with ice and less dense water at less than 4 degrees Celsius in the epilimnion and more dense water at 4 degrees Celsius in the hypolimnion. With thaw out in March or April, there is another brief mixing event before stratification begins again.

Monitoring data from the 2010s suggest that phytoplankton productivity in Curlew Lake is typically phosphorus-limited and occasionally co-limited by phosphorus and nitrogen. Total N:P ratios together with dissolved nutrient concentrations can be used to indicate which nutrient is most limiting to algae growth. Guildford and Hecky (2000) found that ratios greater than 22 indicate phosphorus limitation, ratios less than 9 indicate nitrogen limitation, and ratios between 9 and 22 indicate co-limitation of algae growth by both phosphorus and nitrogen. The elevated dissolved inorganic nitrogen concentrations (about 50 µg/L) and dissolved orthophosphate phosphorus concentrations (about 8 ug/L) observed in the surface waters of Curlew Lake in 2021 (Ecology 2022) together with a total N:P ratio of around 35 (greater than 22) suggests that algae growth in Curlew Lake is limited primarily by phosphorus.

Water Quality Parameters of Interest and Potential Sources

Curlew Lake has suffered toxic algae blooms. These are typically the result of excess nutrients in the lake that can come from both the lake’s drainage and the lake. In some cases, cyanobacteria and algae growth may be influenced by other nutrients (e.g., iron, sulfur), temperature, light availability, and zooplankton grazing. Based on the available historical data, we expect that phosphorus is the limiting nutrient in Curlew Lake and that high levels of phosphorus are the primary cause of toxic algae blooms (see discussion in Section 3.2.2.).
We seek to collect data necessary to construct hydrologic and nutrient (phosphorus and nitrogen) budgets for Curlew Lake. The budgets will give us insight into identifying the key sources of nutrients and potential strategies to control those sources.
We plan to characterize the plankton community and track algal biomass over the year, measured by proxy with chlorophyll concentrations. These data will provide insight into the seasonal ecological succession of the lake. These data, along with nutrient and other water quality data, will be useful in confirming our hypothesis that algae growth is primarily driven by the phosphorus supply.
The suspected sources of phosphorus are:

  • Internal loading from phosphorus-rich sediments

  • Shoreline septic systems

  • Stocking of rainbow trout

  • The four primary lake inlets (Trout, Mires, Barrett, and Herron creeks) are pathways of nutrients arising from:

    • Septic systems

    • Soil erosion

    • Cattle manure

    • Agriculture fertilizer

    • Wildlife (e.g., elk)

We do not anticipate that waterfowl (e.g., ducks and geese) are significant sources of nutrients to the lake.

Project Goals

The goal of this monitoring project is to collect data of sufficient quality and quantity to support the development of a CMP for Curlew Lake by following Ecology’s Lake Cyanobacteria Management Plan template and guidance. Specifically, the data will be used to:

  • Track changes in the water quality characteristics of Curlew Lake throughout one year

  • Quantify the nutrient loading of different sources and inputs of nutrients to Curlew Lake

  • Develop hydrologic and nutrient budgets for Curlew Lake

  • Provide recommendations for cyanobacteria management in Curlew Lake

The objectives of this project are to:

  • Collect monthly surface water quality data from Curlew Lake, excluding months where sampling is unsafe due to ice conditions

  • Collect nine routine water quality sample data from the major contributing creeks

  • Collect three wet-weather water quality samples from the major contributing creeks

  • Collect continuous flow data from Trout Creek and weekly lake level for Curlew Lake

  • Characterize the phosphorus fractions in sediment in Curlew Lake

  • Determine the contribution of nutrients in surface runoff to Curlew Lake

  • Obtain a rough picture of lake macroecology through a collection of data related to aquatic vegetation and human use

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