Wastewater treatment requires the removal of contaminants, solids, nutrients, coliforms, and pathogenic bacteria. Classical treatments require high energy and induce secondary pollution by disinfectants. Alternatively, phycoremediation, which involves the use of algae to clean water, appears smarter and more sustainable because compounds such as nitrogen, phosphorus, sulfur, and minerals appear as ‘nutrients’ to feed algae rather than ‘contaminants’. Phycoremediation thus allows to remove phosphates, nitrates, heavy metals, pesticides, hydrocarbons, nitrogen, and phosphorus. Moreover, the conditions favoring algal growth are disfavoring bacterial growth, which prevents the proliferation of pathogenic bacteria and improves water disinfection. Open pond systems have low maintenance, simple design, and reduce carbon footprint. Here we review factors controlling wastewater phycoremediation, and the most common systems. Microalgae are the main species used for phycoremediation. Efficiency is controlled by biotic factors, abiotic factors and algal strains. Photobioreactors appear unsuitable for large-scale applications due to cost, complicated operational procedures and scaling-up difficulties. Open pond systems are ideal for providing clean water in developing countries.