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October 20, 2022

Auburn Ravine Water Sample Project

Results of Recent Water Tests in Auburn Ravine

On June 15, and October 5, 2022, volunteers with Friends of Auburn Ravine and a representative from the Regional Water Quality Control Board collected water samples from Auburn Ravine Creek using data collection protocols developed by the State Water Resources Control Board. The samples were then analyzed at a Regional Water Quality Control Board lab to estimate the amount of a bacteria called “E.coli” in the water.

Various types of bacteria naturally occur in humans and other warm-blooded animals such as birds, cattle, and otters.  E.coli is one of those.  Some strains of E.coli can cause illness in humans, and high amounts of E.coli in a water body can be an indicator that there might be other dangerous bacteria in the water. 

Water samples were collected at:

  • Hemphill Dam (about 2 miles east of downtown Lincoln)

  • Liberty Lane (about 1 mile east of downtown Lincoln)

  • McBean Park in downtown Lincoln

  • The Lincoln Gauging Station which is near the Auburn Ravine dog park west of Lincoln Blvd.

Per standard procedure, the half-cup water samples from the creek were taken to the lab and divided into multiple containers (48 small, 48 large) along with a growth medium that is conducive to E.coli reproduction.  Those containers were then sealed and allowed to sit in a 95-degree (F) incubator for 20 hours.  At the end of that time, the containers were removed and viewed under ultraviolet light. The positive containers glowed and were counted.

The results were then compared to a statistical table that gives an estimate of how much E.coli there might be in each sample.  That estimate is called the Most Probable Number (MPN).

The MPN was then compared to well-established public health guidelines that indicate which levels of E.coli are of concern.

Here are the results that the lab reported:

*The sample at Hemphill was taken from the canal that leaves the creek just upstream of the streambed alterations that are being done to improve fish passage at that site.

According to the Regional Water Board, results in the 200s are considered somewhat elevated, but do not exceed the limits for water recreation.

You will notice that all the numbers went down from June 15 to October 5 except for the Hemphill site which went up.  On October 5, none of the sites were in the “somewhat elevated” category.

The tests did not include any DNA analysis, so it is not appropriate to assume that the elevated levels were caused by humans.  When DNA tests were done recently on E.coli samples from the American River, it was discovered that much of the E.coli in the American River came from birds.

We will be collecting additional water samples in early November. After the Regional Board’s lab completes their analysis of those samples, we will provide the results.

Friends of Auburn Ravine does not do the tests, and is neither responsible for the results of the tests, nor for interpretation of the results of the tests.

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