A shrimp farmer can easily make a Secchi disk. It is a 20-cm diameter disk painted with alternate black and white quadrants. Traditionally, the disk has been tied to a calibrated line and a weight attached on the underside. However, shrimp ponds are shallow and Secchi disk readings will normally be less than 1 m. An alternate method is to attach a meter stick or calibrated rod vertically in the center of the disk (Fast & Lester, 1992).