Quantifying health in wild marine turtles is challenging because reptiles have characteristically wide-ranging normal reference values for many indicators of health and because of the shortage of population-specific baseline data for wild animals. We measured blood biochemistry profiles (calcium, magnesium, sodium, lactate dehydrogenase (LDH), urea, cholesterol, triglycerides, and glucose) of green turtles (Chelonia mydas) in Moreton and Shoalwater Bays, Australia, and compared them in relation to capture site, age, sex and exposure to harmful algal blooms of the toxic cyanobacteria Lyngbya majuscula. Turtles were considered to be clinically healthy when no external injuries or lesions were observed and there was no evidence of disease or emaciation. Differences in blood profiles were detected between sites, but not between age groups or sexes. Turtles that were exposed to L. majuscula generally had lower plasma glucose concentrations and decreased LDH activity, which may represent a metabolic downregulation resulting from food limitation. This study provides the first blood biochemistry reference values for green turtles in Queensland, Australia, that can be used in future assessments of green turtles in these foraging habitats.