5 hidden hazards of summertime swimming

When refreshing water beckons, millions of people across the United States jump right in. But there's always a possibility of contamination, regardless of whether it's fresh or salt water, chlorinated pools or the neighborhood splash pad.

You may never contract the following illnesses, but they do exist and experts say you should know about them.

Cyanobacteria (toxic algae)

Also known as blue-green algae, cyanobacteria are microscopic organisms found naturally in all types of water (fresh, combined salt and fresh water and marine water), according to the Centers for Disease Control and Prevention (CDC).

Sometimes the algae start to multiply quickly, forming toxic blooms in warm waters that aren’t moving fast and are filled with nutrients, such as fertilizer or septic overflows.

You may be able to see the blooms that spread across the water’s surface and the CDC recommends you and your pets stay away from water that is discolored or has a foamy or scummy surface.

"Cyanobacteria tend to outcompete other algae when water temperatures get above about 20 degrees Celsius (68 degrees Fahrenheit), and they outcompete most other organisms and persist for long periods of time," Beverley Anderson-Abbs, a senior environmental scientist for the California State Water Resources Control Board, said in an email.

Naegleria fowleri (brain-eating amoeba)

It’s important to note that these deadly infections are rare, but they do happen in the U.S. Between 1962 and 2016, the CDC reported 143 known Naegleria fowleri infections, with only four survivors – a fatality rate of more than 97 percent.

The amoeba, a single-celled organism, lives in warm freshwater, such as lakes, rivers and hot springs. These organisms can travel up the nose to the brain and spinal cord as people swim or dive. This can cause a brain infection called Primary Amebic Meningoencephalitis (PAM). CDC researchers said people do not become infected from drinking contaminated water.

Naegleria fowleri is thermophilic, or heat-loving. Most infections occur during July, August and September when there is prolonged heat, higher water temperatures and lower water levels.

Vibriosis (flesh-eating bacteria)

Several cases of Vibrio vulnificus have been confirmed this summer in Mobile County, Alabama. Those affected are recovering, but health officials continue to warn the public about how to avoid soft-tissue infections.

Vibriosis infections can occur when people eat raw or undercooked seafood – particularly oysters – or when an open wound is exposed to warm seawater, according to the Alabama Department of Public Health.

Vibrio bacteria naturally live in certain coastal waters, according to the CDC, and are measured in higher concentrations between May and October.

“If you have open wounds, cuts, abrasions and sores, stay out of [brackish and warm salt water.] Persons with low immune systems, cancer, diabetes, liver disease and other chronic conditions should avoid eating raw or undercooked seafood, especially oysters,” Dr. Karen Landers, assistant state health officer with the Alabama Department of Public Health, said in a statement.

Cercarial Dermatitis (swimmer’s itch parasites)

This itchy rash occurs when you come into contact with water that’s infested with parasites.

According to the American Academy of Dermatology, the parasites burrow into your skin when the water starts to evaporate – not when you are in the water. They cause tingling or burning spots, welts or blisters in the affected areas.

Yvonne Mortensen of Shelley, Idaho, told AccuWeather about her encounter with swimmer’s itch from a recreational swimming area. She said after 20 minutes of swimming and wading, she started to feel an itch on her shoulder. As time passed, she said the itching became more intense, especially on her legs.

“It felt like being pricked with needles all over my body,” Mortensen said in a Facebook message. “Just constantly being stabbed with pins. My legs were the worst...The name 'swimmer's itch' does not convey the experience.”

She said oral and topical medication eventually calmed the rash but her skin was very sensitive for a week.

Cryptosporidiosis (parasites)

This parasitic infection is often found in swimming pools and water playgrounds. Outbreaks occur when swimmers swallow water contaminated with fecal matter.

“Cryptosporidium is the leading cause of outbreaks from recreational water venues,” Brittany Behm, spokesperson for the CDC, said in an email. “It can survive for up to 10 days in properly chlorinated water, making it extremely hard to kill.”

Crypto causes a gastrointestinal illness that lasts for a few weeks. The CDC's preliminary data for 2016 shows at least 32 outbreaks occurred in 13 states, compared to 13 outbreaks reported for 2013 and 16 outbreaks reported for 2014.

Behm said the higher numbers could be due to an actual increase in the number of outbreaks, or it could be related to better surveillance systems and laboratory methods for diagnosis.