The run-up to the Rio 2016 Olympics has been particularly bruising, with fears of the Zika virus, doping scandals, political instability in Brazil, high crime levels, infrastructure struggles, and the recently reignited debate over the city's water sanitation. Headlines over the past week or so have streamed with talk about how “just three teaspoons of water” containing Rio’s raw human sewage would be enough to make even the healthiest of athletes sick.

The Associated Press (AP) reported this was also accompanied with advice from Dr Valerie Harwood, chair of the Department of Integrative Biology at the University of South Florida, to tourists and athletes: "Don't put your head under water."

But what exactly is the risk, and just how sick could you become? A rash and niggling sore throat, or a deathly blood-boiling, flesh-eating tropical disease?

The recent fears were prompted after the AP published their 16-month-long study on the waterways of Rio de Janeiro, where many Olympians – such as sailors, rowers, and swimmers – will be competing. Along with the athletes, they also looked to the seawaters in preparation for the hundreds of thousands of tourists who are expected to flock to the idyllic-looking beaches.

One of the most riddled areas was Rodrigo de Freitas Lagoon, where the Olympic rowing and sailing events will occur, according to the report. A sample taken there in March 2015 as part of the AP investigation found 1.73 billion adenoviruses per liter of water. For perspective, thousands per liter in California would be deemed as worrisome.

Adenoviruses are a wide bunch of viruses that can be responsible for a host of infections, including gastroenteritis, conjunctivitis, respiratory illnesses, cystitis, and skin rashes. Although the illnesses can be pretty unpleasant in the short-term, there have been very few reports of a healthy individual dying from an adenoviruses infection.

Most infections can clear up within a matter of days or weeks without treatment. However, a few studies have pointed out that in some cases, an adenovirus infection can cause long-term brain inflammation in rats. But chances are we’ve all come across adenoviruses in our life numerous times, which has most likely been fought off by our immune system, or has perhaps caused a stomach bug or a couple of days coughing away in bed.