The fifth volume in a series of reports describing the methodology and results of a joint research venture between RAND and the Netherlands Rijkswaterstaat. The POLANO project was founded to help the Dutch government analyze the different alternatives (open, closed, and storm-surge barrier cases) for protecting the Oosterschelde region from North Sea floods. Volume V describes a mathematical model that was developed for estimating the potential for anaerobic (oxygen-free) conditions in the proposed Eastern Basin of the Oosterschelde when the basin is converted from a salt- to a fresh-water lake. This conversion will kill the existing flora and fauna and may temporarily deplete the water of oxygen. Using the model, this report shows that anaerobic conditions vary with the velocity of the wind and the size of the basin. The alternatives that involve a small Eastern Basin are favored.