Open ponds are the most usual setting for large-scale outdoor microalgae cultiva­tion (Fon Sing et al. 2013; Jeffery and Wright 1999). The major commercial pro­duction of algae is today based on open channels (raceway) which are less expensive, and easier to build and operate compared with closed photobioreactors (Borowitzka 2013b; Tredici and Materassi 1992). In addition, the growth of mic­roalgae meets is less challenging in open than closed cultivation systems; however, just a few species of microalgae (e. g. Chlorella, D. salina, Spirulina. sp., Chlorella sp. and P. carterae) have been successfully grown in open ponds (Moheimani and Borowitzka 2006; Tredici and Materassi 1992). Large-scale outdoor commercial microalgal culture has been methodically developed over the last sixty years (Borowitzka and Moheimani 2013a). Profitable production of microalgae, at present, are limited to a comparatively few small-scale (<10 ha) plants producing high-value health foods, most located in south-east Asia, Australia and the USA (Benemann 1992; Borowitzka and Borowitzka 1990; Richmond 1992). Two major types of large-scale open cultivation systems have been developed and have been used on a commercial basis. These are (a) unstirred ponds and (b) stirred ponds (circular and raceway) (Borowitzka 1993a, b; Borowitzka and Moheimani 2013b). The most common commercial microalgal culture system in use today is the paddlewheel-driven raceway pond (Richmond et al. 1993). The advantages and disadvantages of growing microalgae in open ponds and closed photobioreactors are summarised in Table 1.2. Relatively low cost of construction and operation are the main reasons for culturing algae in open ponds (Tredici and Materassi 1992). However, the high contamination risks and low productivity, induced mainly by poor mixing regime and light penetration, are the main disadvantages of open systems.