How are coliforms found in ocean-dwelling shellfish linked to Langley?

Coliforms are bacteria that can be found in organic material such as plants and the soil, and the intestines of humans and warm-blooded animals (fecal coliforms). High levels of coliforms can pose a risk to human and environmental health.

Shellfish can quickly become contaminated and unsafe for consumption when bacterial levels are high. Contamination occurs when shellfish absorb pollutants or toxins found in the water. This contamination can come from a point source or non-point source pollution.   

Point-source pollution is defined as pollution entering the water system from a location where the output of the pollution can be measured, such as a wastewater treatment and collection system. Non-point source pollution is defined as pollution entering the water system at random locations that are difficult to measure, such as throughout a watershed. Non-point sources range from natural processes, to human activities, such as urban stormwater and agriculture runoff.

Point and non-point pollutants entering water: WWTP, Industry, Fecal coliforms, marine aquaculture, toxic algae.
Figure 1: Point source and Non-point source pollution entering shellfish harvesting areas. Source
An image of sources of coliforms: leaking sewer lines and stormwater runoff, septic and pet waste, farm animal waste, wildlife waste.
Figure 2: Different types of fecal coliform sources that can enter a water way: Leaking sewer lines, storm water runoff, septic waste, pet waster, agriculture waste, wildlife waste. Source

How are the coliforms found in Langley watersheds linked to the ocean? When runoff and other bacterial sources enter the local waterways of Langley, coliform levels can increase dramatically. The waterways of Langley eventually drain into 4 major rivers: the Fraser River, the Nicomekl River, and the Nooksack River in Washington, USA. These rivers eventually drain into the ocean at the Strait of Georgia, Semiahmoo Bay, Mud Bay, and Bellingham Bay. Any fecal coliforms that are still alive at this point of transport have floated down the waterways from their initial source point and make their way into the ocean.

What determines how many coliforms survive? Coliforms are temperature dependent and may die-off if environmental conditions are not favorable.  During winter, the cold water temperatures will kill coliforms. Similarly, the hot UV rays during summertime will do the same. During more favorable conditions, large amounts of these bacteria can survive all the way to the ocean.   

The build-up of coliforms in ocean waters leads many shellfish harvesting sites to close. The BC Centre for Disease Control has created a map (Figure 3) that shows active shellfish harvesting sites for BC. On this map, users can check which areas are open for harvest and see if a harvesting site is closed due to contamination.

Snapshot of the current Shellfish Harvesting Status Map. Some areas are closed due to high levels of coliforms in the water.
Figure 3: Snapshot of the current Shellfish Harvesting Status Map. Obtained on March 16, 2022, from

The health of waterways in Langley has a huge impact on not only the local area, but nearby shorelines as well. Reducing the impact of human activity on aquatic ecosystems is a vital step in ensuring safe shellfish harvesting. Interested in learning more about topics that affect watershed health? LEPS will be hosting a series of webinars on a variety of these topics. Check out the LEPS Calendar to find out more!