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Seawater contains hundreds of viruses, revealed with dye in the flask on the right. Most are harmless, but some microbes living under the sea and amid the sand aren't. (Photo: © Karen Kasmauski/Corbis)

Eight Diseases To Watch Out For At the Beach

Forget sharks: These potentially deadly pathogens and parasites can lurk in sand and sea

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Bloomin’ Algae

(© Kevin Schafer/Corbis)

Most algae living in the surface waters of oceans and lakes are pretty tame. But some algae produce nasty toxins. This becomes a bigger problem when runoff carries nutrients like nitrogen and phosphorus into waterways and triggers population explosions known as blooms. Harmful algal blooms can poison shellfish and contaminate regional drinking water. Swimmers can inhale algal toxins through water vapor, swallow them or absorb them through the skin.

In freshwater, the biggest concern is blue-green algae, or cyanobacteria, which likely caused 11 of the disease outbreaks reported to the CDC between 2009 and 2010. Some strains of cyanobacteria produce toxins that can damage your liver, while others target the nervous system. According to the CDC report, just touching the algae produced rashes, swelling and skin sores. Swimmers who ingested or inhaled contaminated water got a range of symptoms such as diarrhea, nausea, cramps, coughing, wheezing, congestion and ear infections. 

In saltwater ecosystems, dinoflagellate algae like Karenia brevis are the main culprits behind harmful blooms called red tides. K. brevis produces brevitoxins, chemicals that disrupt nerve cell signaling. For swimmers this may translate to trouble breathing, sore throats and irritated eyes.

About Helen Thompson
Helen Thompson

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.

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