--- title: Why July Is the Most Dangerous Month To Go Swimming description: Swimming in oceans, lakes and rivers caused 140 disease outbreaks and almost 5,000 illnesses between 2000 and 2014, the CDC says. canonical: https://time.com/5325136/swimming-untreated-water-disease-outbreaks/ author: Jamie Ducharme article:opinion: false article:content_tier: free article:published_time: 2018-06-28T17:33:46.000Z article:modified_time: 2026-08-04T07:53:21.042Z article:section: Health og:title: Why July Is the Most Dangerous Month To Go Swimming og:description: Lakes, rivers and oceans are linked to disease outbreaks, finds the CDC og:url: https://time.com/5325136/swimming-untreated-water-disease-outbreaks/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt78f795f7ac069979/6989342322fb8571f6e2606c/swimming-lake.jpeg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 7200 og:image:height: 4050 og:image:alt: Person swimming in lake og:type: article twitter:card: summary_large_image twitter:title: Why July Is the Most Dangerous Month To Go Swimming twitter:description: Lakes, rivers and oceans are linked to disease outbreaks, finds the CDC twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt78f795f7ac069979/6989342322fb8571f6e2606c/swimming-lake.jpeg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # Why July Is the Most Dangerous Month To Go Swimming > Sponsored content. 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Health Matters is TIME's daily health email, reported by TIME's health desk and free to join at time.com/newsletters. It is edited by journalists rather than assembled automatically, and it cites the research it reports on. #### Is Health Matters free? Yes. Health Matters is a free daily newsletter from TIME, available at time.com/newsletters. #### Who reads TIME's Health Matters newsletter? Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators. ## Video: Norovirus Is the Worst. Here's What to Know About It [Watch (HLS stream): Norovirus Is the Worst. Here's What to Know About It](https://cdn.jwplayer.com/manifests/Caz7IQD3.m3u8) (1:34)  _Published 2017-07-19. Chipotle confirmed on Tuesday that multiple customers were sickened after eating at a location in Sterling, Va., reporting symptoms consistent with norovirus. Also known as the winter vomiting bug._  by [Jamie Ducharme](https://time.com/author/jamie-ducharme/)  ## Jamie Ducharme Ducharme is a contributor to TIME. Jun 28, 2018 5:33 PM UTC  Person swimming in lake Person swimming in lake Johner Images—Getty Images/Johner RF  by [Jamie Ducharme](https://time.com/author/jamie-ducharme/)  ## Jamie Ducharme Ducharme is a contributor to TIME. Jun 28, 2018 5:33 PM UTC Just in time for [swimming season](http://time.com/4688623/swimming-pool-health-benefits/), the Centers for Disease Control and Prevention (CDC) has issued [a new report](https://www.cdc.gov/mmwr/volumes/67/wr/mm6725a1.htm) on disease outbreaks associated with swimming in rivers, lakes and oceans. Between 2000 and 2014, public health officials in 35 states, plus Guam, reported a total of 140 disease outbreaks associated with swimming in untreated recreational waters — mainly at beaches and bodies of water in public parks, the report says. These outbreaks led to 4,958 illnesses and two deaths. The vast majority of outbreaks with a confirmed cause were linked to gastrointestinal pathogens such as [norovirus](http://time.com/4864685/norovirus-outbreak-what-to-know/), Shigella and E. coli. People typically get sick from these illnesses when they accidentally ingest water contaminated by fecal matter. Such contamination can happen through wastewater and sewage runoff, flooding or someone defecating while swimming, the report says. Most of the remaining outbreaks were caused by parasites transmitted by birds present in recreational waters, toxins and chemicals or harmful algal blooms, the report says. The two deaths were caused by Naegleria fowleri, a rare type of freshwater ameba that enters the nose and destroys brain tissue. The majority of outbreaks struck between June and August, and nearly 60% happened in July. Swimmers may be at a lower risk of infection if they stick to “well-operated, treated recreational water venues,” the report says — although [a prior report from the agency](http://time.com/5280710/hotel-pools-spread-disease/) also detailed plenty of disease outbreaks that could be traced back to hotel pools, hot tubs and other treated recreational waters. Those who choose to [swim in untreated waters](http://time.com/5159851/why-people-are-swimming-in-freezing-water/) should use caution in those that are shallow, poorly circulating, over-crowded, far from toilets and other hygiene facilities or frequented by young children with “no or limited toileting skills,” the report says. Swimmers should also steer clear of water that’s “discolored, smelly, foamy or scummy” and avoid swimming after high rains or floods, according to the CDC. To reduce disease transmission, the CDC says people should avoid entering public waters if they’re sick and do their best to avoid swallowing water while swimming. Organizations that maintain swimming areas should also try to minimize flooding and runoff contamination, keep wildlife away from swimming areas as much as possible and regularly monitor aquatic bacteria levels, the CDC says. ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/5325136/swimming-untreated-water-disease-outbreaks/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/5325136/swimming-untreated-water-disease-outbreaks/"},"headline":"Why July Is the Most Dangerous Month To Go Swimming","datePublished":"2018-06-28T17:33:46.000Z","dateModified":"2026-08-04T07:53:21.042Z","description":"Lakes, rivers and oceans are linked to disease outbreaks","url":"https://time.com/5325136/swimming-untreated-water-disease-outbreaks/","keywords":["Public Health","onetime","healthytime"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt78f795f7ac069979/6989342322fb8571f6e2606c/swimming-lake.jpeg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Jamie Ducharme","jobTitle":"Ducharme is a contributor to TIME.","url":"https://time.com/author/jamie-ducharme/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt78f795f7ac069979/6989342322fb8571f6e2606c/swimming-lake.jpeg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"Person swimming in lake","caption":"Person swimming in lake","creditText":"Johner Images—Getty Images/Johner RF","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/public-health/","name":"Public Health"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/5325136/swimming-untreated-water-disease-outbreaks/","name":"Why July Is the Most Dangerous Month To Go Swimming"}}]},{"@context":"https://schema.org","@type":"VideoObject","name":"Norovirus Is the Worst. 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