Beaches and parks along Lake Washington provide a great environment for outdoor activities and relaxation for residents nearby. But on May 22nd, 2019, the beach at Magnuson Park was closed to people and pets because of the high E. coli concentration found in the water during a routine water quality test done by King County.
Based on the published data, the test was conducted on May 20th, and the concentration found was 4,733 CFU (Colony-Forming Units) per 100 milliliters of water. This concentration exceeds the King County beach closure criteria (day’s average E. coli over 1000 CFU/100 ml) by 4.7 times. Thankfully, the park has been re-opened after the following two water quality test indicated a lower E. coli concentration.
E. coli is an abbreviation of Escherichia coli. The concentration of E. coli is often used as a water quality index where higher concentrations indicate a higher risk of getting sick when performing activities in the area. E. coli is most commonly found in feces, thus having a high E. coli concentration in a water sample usually means there were feces nearby the sample location, which could be from humans, dogs, birds or other animals.
Usually the action for lowering the E. coli concentration value is finding and cleaning up the source of contamination. By doing so, it restricts the availability of nutrients for E. coli to grow and survive. However, several water properties can also be crucial towards the growth of E. coli colonies in open environments. Temperature, pH, dissolved oxygen and dissolved organic carbon are all important factors affecting the survival rate. In general, higher temperature and pH values increase the E. coli decline rate, as do lower amounts of dissolved oxygen and dissolved organic carbon. It is also known that E. coli favors a more stable environment, while large fluctuations in the environment often increases the stress level.
Although it may be hard to predict the amount or the fate of E. coli colonies inside an open waterbody, having a general sense of how those important water properties (temperature, pH, dissolved oxygen and dissolved organic carbon) vary over time can still provide a general picture of how long E. coli might persist. A model of Lake Washington with the capability to model temperature can be downloaded from the EEMS website and run with the demo version of EEMS. We encourage users to download the model, take a look at the model result or even make some changes. If there are any problems or question about the model, feel free to post questions on the forum, our staff or other EE users will be happy to answer your questions.
Find more information about the survival of E. coli in the article bellow,
Survival of Escherichia coli in the environment: fundamental and public health aspects
