City staff tests for E. coli at the Crystal Lake public swimming beach from Memorial Day through Labor Day.  If the level exceeds the standards set by the Minnesota Pollution Control Agency (MPCA), the beach will be closed temporarily until the readings return to a safe level.  Information about the Minnesota state rule referencing E. coli levels for recreational waters is found below:

Minnesota Rule 7050.0222 Specific Water Quality Standards for Class 2 Waters of the State; Aquatic Life and Recreation:  E. coli levels not to exceed 126 organisms per 100 milliliters as a geometric mean of not less than five samples representative of conditions within any calendar month, nor shall more than ten percent of all samples taken during any calendar month individually exceed 1,260 organisms per 100 milliliters. The standard applies only between April 1 and October 31.

The entire rule regarding water quality for recreational waters in Minnesota can be found here:
Minnesota Rule for Recreational Water Quality Standards.

What is E. coli?

E. coli is short for Escherichia coli, the scientific name for a group of bacteria found in the intestines and feces of warm-blooded animals such as mammals and birds.  While most of the hundreds of strains of E. coli are harmless (one notable exception associated with food contamination is E. coli O157:H7), their presence can indicate sewage or feces-contaminated water which may include pathogens (disease-causing organisms).

Direct testing for pathogens is expensive and impractical, as pathogens are rarely found because they usually occur sporadically and at low levels.  Instead of testing for the pathogens themselves, public agencies test for the presence of “indicator” species, so called because their presence indicates that sewage or fecal contamination may have occurred. The two most commonly used indicators for recreational waters are fecal coliforms and E. coli.

Interpreting the Results

Three samples are collected weekly from Crystal Lake beach with results listed in the table below.  The results are given in units of E. coli bacterial colony forming units (CFU) per 100 milliliters (ml) of water (Table 1).  If E. coli levels exceed those listed by the state (see above), the beach will be closed temporarily until further testing shows safe levels.

For more information, call 952-895-4500.


Table 1. E. coli Test Results for Crystal Lake Beach. Results are given in CFU/100 ml, and geometric means are calculated from last five samples.

	Sample 1		Sample 2		Sample 3
DATE	Single sample	Geometric mean	Single sample	Geometric mean	Single sample	Geometric mean
May 29, 2012	31	-----	50	-----	48	-----
June 4, 2012	5	-----	2	-----	10	-----
June 11, 2012	6	-----	8	-----	18	-----
June 18, 2012*	2000	-----	1920	-----	900	-----
June 20, 2012	50	39.2	120	45.0	120	56.6
June 25, 2012	14	33.5	8	31.2	0	0.7
July 2, 2012	17	42.8	18	48.4	11	0.7
July 9, 2012	18	53.3	16	55.6	10	0.6
July 16, 2012	80	28.0	150	33.4	90	0.4
July 23, 2012	20	23.3	25	24.4	25	0.3
July 30, 2012	125	36.1	75	38.2	30	23.7
August 6, 2012	76	48.7	20	39.0	15	25.2
August 13, 2012	20	49.7	30	44.2	70	37.2
August 20, 2012	15	35.6	15	27.9	15	26.0
August 27, 2012	60	44.3	30	28.9	4	18.0
---	---	---	---	---	---	---

* Heavy rains caused temporary spike in E. coli.