Background Most cultures of algae today are grown as monocultures. The primary reason for this appears to be that specific strains of algae contain the high-value products that are desired for harvest. But, in algae cultures grown primarily for lipid production, or as a stage in wastewater remediation, mixed algae cultures may mitigate environmental risk. Results Four-strain mixed cultures of algae were grown in simulated wastewater, alongside the monocultures, under different temperature and lighting conditions. Under all conditions the mixed cultures were less productive than the most fit monocultures for each situation, but more productive than the least fit monocultures. Statistical analysis based on an exponential growth model of the monocultures also suggested that mixed cultures are actually more productive both in terms of biomass and lipids than simply the sum of the monocultures. Conclusuions A mixed culture composed of various similarly productive strains with various optimal growing conditions would be less susceptible to environmental shifts than a monoculture. This study demonstrated the promise of an appropriately defined mixed culture to reduce risk in applications such as wastewater remediation and lipid production that do not rely on specific strains containing high value products. (c) 2012 Society of Chemical Industry