Why can’t we have algae farms in the Sahara?

Title says it all. I have been doing independent research on the matter, but I truly cannot see, from a theoretical perspective, why we cannot flood many of the small depressions in the Sahara below sea level (I say [relative] small ones, which are near the sea, not massive ones inland) in order to farm oxygen using the various species of plankton? There is ample sunlight, land which is deep enough to let light get through but not too deep, and lots of local phosphate supplies. Has anyone seen any studies or research in this field? I have looked for journals but they are quite light