Aim: To determine the cause of a disease known variously as "Barcoo fever, Barcoo spews, Barcoo sickness", or simply "the Barcoo", once prevalent in outback northern and central Australia.
Method: Comparison of the recorded symptoms with those of known infectious diseases and gastrointestinal illness; consideration of the epidemiology, including times and places of occurrence and the population affected.
Result: The disease had features of a toxic rather than an infectious illness and had the characteristics of poisoning by toxic cyanobacteria (blue-green algae). In particular the symptoms were similar to those shown to be due to the hepatotoxin of the tropical cyanobacterium Cylindrospermopsis raciborskii (Woloszynska).
Conclusion: Poisoning by cyanobacterial toxins was once widespread in outback northern Australia and toxic cyanobacteria must still be present in many areas. Although not reported and probably not diagnosed as such, the disease still occurs in mild form. Widespread illness does not occur but individuals still experience symptoms similar to those described a century ago. Precautions are necessary to prevent algal contamination or proliferation in domestic or communal water supplies.