Lake Minnetonka Conservation District

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Big Island Illness Investigation Update 07/18/2019

This is an update to the investigation regarding illnesses at Big Island, Lake Minnetonka, occurring over the 4th of July. The Hennepin County Public Health Department (HCPH) and Minnesota Department of Health (MDH) held a press conference on July 12, 2019. As of July 18, 2019 no additional illnesses have been reported and they consider the investigation completed.  We appreciate the cooperation of all the involved individuals in working with the health departments since we understand this was not a pleasant experience.  

Lake Minnetonka is one of the largest and busiest lakes in Minnesota with 42 bays and 14,000 acres. The 4th of July holiday is one of the busiest holidays, with an estimated 7,000- 9,000 boaters on the lake on the 4th.  The media coverage helped spread the word so a thorough illness investigation could occur. Many outbreaks throughout the country are underreported or not reported at all.

Tips for Preventing Recreational Water Illnesses

Safety Tips for While the cause was not determined, the LMCD will be reviewing the situation, best practices and possible options. It is important that everyone does their part to protect the lake and ensure the health and safety of all those who enjoy the lake. More summer lake safety and beach tips can be found at

The HCPH and MDH emphasized the importance of good safety practices when at the lake or beach such as:

  • Do not go into the water if you are sick
  • Don’t drink the water
  • If possible, shower before and after swimming
  • Boaters should take regular breaks to use appropriate toilet facilities
  • Don’t prepare food when you are sick
  • Wash hands frequently
  • Use basic prevention practices

Summary of Illness Investigation

The following is a brief summary of the information presented by HCPH and MDH at the press conference on July 12, 2019 regarding their findings of the illness investigation.

  • The illnesses occurred in or near the Big Island on July 4th and no new illnesses were reported.
  • Based on the illness characteristics, it was considered an illness outbreak. 172 individuals of 225 individuals reported vomiting and diarrhea. The symptoms usually lasted 24-48 hours, but some lasted several days. There was a gamut of ages, but predominantly mid 20s to 30s. While there was no evidence of person to person transmission from the incident, it could be transmitted in that manner even after the initial incident.
  • Lab results were inconclusive and were based on testing for 22 of the most common bacteria, viruses, and parasites.
  • They did not believe there was ongoing illness or further risk to the public from this incident.
  • The beach closings around the county are unrelated to the illness investigation and are based on routine water testing that checks for potential water quality concerns. The type of E. coli used as an indicator organism for beach water testing purposes can have many sources such as animals, soil, etc. It is not necessarily the specific type of E. coli that is known to cause gastrointestinal illness. These beach closures are preventive.

The following is a summary of answers to questions:

  • It is not unusual to see illnesses this time of year due to Minnesota waters. The runoff from rain and high water temperatures contributes to the risk.
  • We all need to do our part to keep the waters clean.
  • The last time there was a large illness was in 2012 at a water park involving approximately 100 people.
  • Based on the illness characteristics and symptoms, this outbreak was not considered medically serious and most individuals improved within a couple of days.
  • Some reports were where people ate or drank items not normally consumed.
  • Some calls came in Monday morning, but with the media attention and the word out, many more calls were received.
  • Many types of possible exposures were considered. While it could be one person defecating in lake, the introduction of feces increases normally with the congregation of a lot of people. It is tough to know the source. It could be a combination of things. While urine isn’t the suspect, we encourage people to use proper toilet facilities on a boat or land facilities.
  • It was a very localized event and there is always a risk where you have a lot of people.
Posted on: July 19th, 2019