Blackwater fever is a complication of malaria characterized by intravascular haemolysis, haemoglobinuria and kidney failure. Blackwater fever is caused by heavy parasitization of red blood cells with Plasmodium falciparum. When the red blood cells burst, haemoglobin leaks into the blood plasma. This free haemoglobin damages the glomerulus in the kidney, and begins to leak into the urine where it causes further damage to the tubules of the kidney.

The presence of haemoglobin in the urine (haemoglobinuria) causes a dark discolouration, hence the name. When it comes out of the penis the color is black

The treament is antimalarial chemotherapy, intravenous fluid and sometimes supportive care such as intensive care and dialysis.

Blackwater fever is a serious complication of malaria, but cerebral malaria has a higher mortality rate. Blackwater fever is much less common today than it was before 1950. It may be that quinine plays a role in triggering the condition, and this drug is no longer commonly used for malaria prophylaxis. Quinine remains important for treatment of malaria.