Siltcoos Lake (Douglas, Lane)

Reachcode: 17100207000082 | Area: 3130.7 acres | Shoreline: 31.4 mi | View on Interactive Map

Siltcoos Lake is a large (1280 hectares), shallow (mean depth 3.3 m; maximum depth 6.7 m) lake located on the Central Oregon Coast, just south of Florence and bordered by Dunes City, Oregon.  The outflow and water level of Siltcoos Lake is regulated by a dam on the Siltcoos River 4 km upstream from the Pacific.  Several permanent streams feed the lake from its 176 square kilometer watershed including Fiddle Creek, Maple Creek, and Woahink Creek, the outflow from Woahink Lake.  Much of the watershed is forested and used for timber harvest, residential development, and limited agricultural production. 
The lake is popular for recreational activities, particularly fishing for wild coastal Coho salmon, rainbow trout, cutthroat trout, largemouth bass, bluegill, crappie, and yellow perch (Buckman 2004). The lake is also the domestic drinking water source for approximately 125 of the 1330 residents of Dunes City and numerous residents outside the city limits within Lane and Douglas Counties (LCOG 2002).
During the fall of 2007 a dense bloom of the potentially toxigenic blue-green algal species Anabaena planktonica prompted Dunes City, the South Coast Water District, the Lane County Health Department, and the Oregon Department of Human Services to issue an advisory against usage of Siltcoos Lake water for drinking and other domestic use (DHS 2007). Residents dependent upon Siltcoos Lake were forced to find alternate domestic water sources for a total of 52 days.  This incident was part of a long history of water quality problems including dense algal growth and excessive growth of the non-native aquatic macrophytes Brazilian elodea (Egeria densa), parrotsfeather (Myriophyllum aquaticum), and two-leaf water milfoil (Myriophyllum heterophyllum) (Pfauth and Sytsma 2005; Johnson et al. 1985; McHugh 1979). Because of the water quality problems, the Oregon Department of Environmental Quality (DEQ) placed the lake the 303(d) list of impaired water bodies; specifically due to violations of the “aquatic weeds and algae” water quality criterion (DEQ 1998; DEQ 2006).  
Dunes City has acted on water quality concerns for both Siltcoos and Woahink Lakes by issuing a temporary building moratorium (Dunes City 2006a), a septic tank maintenance ordinance (Dunes City 2006b), and an ordinance limiting phosphorus use (Dunes City 2007). Preliminary assessments (Johnson, et al. 1985, LCOG 2002) indicate multiple sources of water quality problems including excess nutrient and/or sediment loading from residential development, poorly functioning on-site septic systems, private forestry and agricultural practices and introductions of non-native aquatic plant species.
Water quality monitoring by the City of Dunes City, Portland State University indicate that the lake is mesotrophic to eutrophic based on water clarity, chlorophyll a concentrations, and total phosphorus concentrations. 

The list below includes results of zebra and quagga mussels surveys conducted by the Center for Lakes and Reservoirs and other agencies. The results "non-detect" and "results pending" indicate that surveys for zebra and quagga mussels were conducted, but none were detected or results are pending. For more details on zebra and quagga mussel monitoring, please visit the Online Mussel Monitoring Map.

Date Status/Species Source
May 16, 2009 non detect Portland State University

The list of plants below includes results of aquatic plant surveys conducted by the Center for Lakes and Reservoirs as well as aquatic invasive plant species detections that have been reported to iMap Invasives: an online, GIS-based invasive species reporting and querying tool.

Plants listed in the table below are categorized as native to Oregon, on the Oregon Department of Agriculture’s (ODA’s) Noxious Weed List, on the Federal Noxious Weed List, or non-native but not listed as noxious. Federal Noxious Weed List plants are plants determined by USDA to be serious threats to U.S. agriculture, irrigation, navigation, public health or the environment (7 C.F.R. 360.200). The ODA Noxious Weed categories are:

ODA Class A - weeds either unknown or with small enough infestations to make eradication or containment possible; targeted for eradication or intensive control.

ODA Class B - regionally abundant weeds (may have limited distribution in some counties); targeted for local/regional control on case-by-case basis.

Download the complete dataset as a CSV

Date Species Status Source
Aug. 4, 2004 Cabomba caroliniana (fanwort, Carolina fanwort) Non-native IMAP
Aug. 4, 2004 Nymphaea odorata (fragrant waterlily) Non-native IMAP
Aug. 4, 2004 Egeria densa (South American waterweed, Brazilian elodea) Non-native ODA Class B IMAP
Oct. 4, 1952 Egeria densa (South American waterweed, Brazilian elodea) Non-native ODA Class B IMAP
April 10, 1952 Egeria densa (South American waterweed, Brazilian elodea) Non-native ODA Class B IMAP
Sept. 29, 1951 Egeria densa (South American waterweed, Brazilian elodea) Non-native ODA Class B IMAP
Jan. 1, 1947 Egeria densa (South American waterweed, Brazilian elodea) Non-native ODA Class B IMAP
Feb. 1, 1946 Egeria densa (South American waterweed, Brazilian elodea) Non-native ODA Class B IMAP
Jan. 2, 1946 Egeria densa (South American waterweed, Brazilian elodea) Non-native ODA Class B IMAP
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