Fecal bacteria levels are elevated in several Skagit County waterways this summer, with officials investigating potential sources of pollution following an unusually warm and dry June.
According to Skagit County Public Works, the highest fecal coliform counts were recorded at Little Indian Slough, upper Thomas Creek, Colony Creek, lower Coal Creek, and upper Hansen Creek during routine water quality monitoring. Samples from No Name Slough and Sullivan Slough each measured 350 MPN (Most Probable Number), well above the state freshwater quality benchmark of 100 MPN per 100 milliliters.
“While high bacteria levels are often linked to rainfall and runoff, they can also increase in the summer due to lower water levels and greater concentrations,” the county said in a water quality update. Increased recreation, agriculture, and wildlife activity can also contribute to bacterial pollution, especially in warm, sunny conditions that help bacteria survive and multiply.
June’s average maximum temperature at the Mount Vernon AgWeatherNet station was 69.9 degrees — about 2 degrees above normal — with just 0.75 inches of rainfall, nearly an inch below average. Warm, dry weather and low water levels can lead to more concentrated bacteria in surface waters, and increased summer recreation, agricultural activity, and wildlife can all contribute to higher contamination levels.
During routine sampling on July 1, the following fecal coliform results were recorded near La Conner (in Most Probable Number per 100mL):
- No Name Slough (Bayview-Edison Rd): 350 MPN
- Sullivan Slough (La Conner-Whitney Rd): 350 MPN
- Big Indian Slough (Bayview-Edison Rd): 170 MPN
- Skagit River – North Fork (Moore Rd near Rexville): 23 MPN
- Swinomish Channel (County Boat Launch): 7.8 MPN
These results exceed the Washington State freshwater quality benchmark for fecal coliform, which calls for an average of less than 100 MPN, with no more than 10% of samples over 200 MPN.
