The water quality of the Seto Inland Sea has improved due to a decrease in the inflow load of nitrogen, phosphorus, and other elements. However, at the same time, the oligotrophic conditions are created, and have resulted in a dramatic fall in fish and shellfish production. With the revision of the Law Concerning Special Measures for Conservation of the Environment of the Seto Inland Sea, direction has been provided for a reorientation towards the Seto Inland Sea as a cultivable "garden" or "farm." This article proposes an effective use of oyster shells as a possible tool in successfully achieving both of these.