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But even with chlorine, swimming pools can act as giant petri dishes for bacteria like E. coli, which lives in the stomach and can cause nausea, stomach cramps, and diarrhea. The CDC analyzed 2008 data from 121,020 routine inspections and found that one in eight pools had been immediately closed for serious violations, like not having any disinfectant in the water at all.

Another 2012 CDC analysis of public pools found that over half of the "pool filter samples tested positive for E. Coli ... a marker for fecal contamination." Another strain of bacteria that can cause skin rashes and ear infections called pseudonmonas aeruginosa was also detected in 60% of the samples.

That goes for ponds and lakes, too

(Flickr/Donald Lee Pardue)

Freshwater lakes and rivers can also be hotbeds for viruses, bacteria, and amoebae. Last July, "70 people who swam in a lake near Portland were sickened by norovirus," according to CBS News. Over half of them were between the ages of seven and 10. Norovirus, which is highly contagious, can cause diarrhea, stomach cramps, and vomiting.

The CDC reports that how the lake became contaminated is unknown, but suggests that if a swimmer with norovirus vomited or had "a fecal incident in the lake." According to the report, "there is evidence that noroviruses can survive in water for several months and probably years."

A rare, brain-eating amoeba called Naegleria fowleri is another danger lurking in warm freshwater lakes and rivers. It's been known to infect people by swimming up their nasal passages. Once inside, it can travel to the brain and cause a fatal infection of the central nervous system called primary amebic meningoencephalitis. Death tends to happen two weeks after infection. "The disease progresses rapidly," the CDC notes, "so [the] diagnosis is usually made after death."

As terrifying as the tiny amoeba is, it is extremely rare, which is true for other types of swimming-related bacterial infections as well. Between 2005 and 2014, only 35 such infections have been reported, according to the CDC. Contrast that with the number of times Americans go swimming in pools or other bodies of water — 301 million times every year.

Avoid deadly animals

It's easy enough to avoid the tiny creatures that could kill you in the water: stay out of the water — or at least don't inhale or drink it. But about 200 people a year fall to deadly wildlife, according to the Washington Post.

An analysis of CDC data between 2001 and 2013 by the Washington Post determined that bears, alligators, and sharks each kill an average of 1 person a year. More seemingly innocuous animals like cows, dogs, and other mammals kill a combined total of about 100 people a year.

Cows, surprisingly, account for approximately 20 deaths a year, targeting mostly cattle handlers on farms.

Avoid deadly insects

Bears, sharks and snakes have nothing on the smallest, most dangerous killers in the animal kingdom — insects.

Bees, wasps and hornets kill an average 58 people a year through anaphylactic shock, the Washington Post notes.

But mosquitoes are the most dangerous animal in the world, killing about 725,000 people worldwide, according to the Smithsonian. Malaria, transmitted by mosquitoes, can cause fever, chills, nausea, and vomiting. Severe malaria can cause organ failure and serious neurological symptoms like seizures, coma, and death.

Luckily, malaria has been all but wiped out in the United States. The 1,500-2000 cases reported every year tend to occur in recent travelers, according to the CDC.

There's also ticks, which are arachnids (not insects) and the primary transmitters of Lyme disease. They're most active in the Northeast and upper Midwest during the spring and the early summer, clinging to leaves and grass. Ticks are extremely tiny and attach themselves in hard-to-see areas of the body like the groin, armpit, or scalp. Infected bites will often have a red, expanding rash that looks like a target.

Lyme disease is rarely deadly but can cause facial palsy, headaches and stiffness due to meningitis, and pain and swelling in the joints. In some cases, people who have been treated for Lyme complain of symptoms long after treatment.

Both ticks and mosquitoes can be avoided to some extent with insect spray; covering up or avoiding grassy areas where ticks may be hiding is probably wise.

Stay indoors during thunderstorms.

(Don Miller/Flickr)

You planned a perfect Fourth of July outing but the weather forecast says that thunderstorms are likely. Do you let the weather forecast mar your day or do you soldier on? In some cases it's probably best to stay indoors.

According to National Geographic, "the fourth of July is historically one of the most deadly times of the year for lightning in the US." Lightning deaths and injuries typically increase in the summer months.

In 2014, 26 people died from lightning strikes. All these deaths occurred between the months of May and October, with the highest rate of fatalities occurring in July, according to the National Oceanic Atmospheric Administration.

Lightning remains an extremely rare cause of death.

Careful handling those fireworks

If you want your summer to go out with a bang, it's probably best to let the professionals handle it. According to the U.S. Consumer Product Safety Commission, fireworks caused an estimated eight deaths and 11,400 injuries in 2013, an increase of 8,700 injuries from the previous year.

The majority of these occurred in the 30 days around the Fourth of July. The report goes on to say that the deaths only occurred with "banned, professional, or home-manufactured device[s]." To ensure safety, it's best to purchase only legal fireworks, and to move away from them quickly once lit — or just leave them to the professionals.

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